Koji-Fermented Maple Custard with Charcoal Shell Recipe
A delicate black charcoal pastry shell cradles a silky, umami-rich koji-fermented maple custard, offering an intriguing balance of earthy depth and subtle sweetness.
Ingredients
<ul class="ingredients-main-list"><li class="ingredients-single-item">For the Koji-Fermented Maple Custard:</li><li class="ingredients-single-item">300ml heavy cream</li><li class="ingredients-single-item">150ml whole milk</li><li class="ingredients-single-item">100g koji rice (shio koji or amazake koji)</li><li class="ingredients-single-item">80ml pure maple syrup (grade A dark)</li><li class="ingredients-single-item">1 vanilla pod, split and seeds scraped</li><li class="ingredients-single-item">6 large egg yolks</li><li class="ingredients-single-item">25g caster sugar</li><li class="ingredients-single-item">Pinch of sea salt</li><li class="ingredients-single-item">For the Charcoal Shell:</li><li class="ingredients-single-item">200g plain flour</li><li class="ingredients-single-item">30g almond flour</li><li class="ingredients-single-item">5g food-grade activated charcoal powder</li><li class="ingredients-single-item">120g cold unsalted butter, cubed</li><li class="ingredients-single-item">75g icing sugar</li><li class="ingredients-single-item">1 large egg</li><li class="ingredients-single-item">2g salt</li><li class="ingredients-single-item">For Assembly:</li><li class="ingredients-single-item">15ml maple syrup for glazing</li><li class="ingredients-single-item">5g edible gold dust (optional)</li></ul>
Equipment
<ul class="equipment-main-list"><li class="equipment-single-item">6 individual tart tins (10cm diameter)</li><li class="equipment-single-item">Food processor</li><li class="equipment-single-item">Fine mesh strainer</li><li class="equipment-single-item">Digital thermometer</li><li class="equipment-single-item">Ceramic fermentation crock or glass container</li><li class="equipment-single-item">Baking beans or pie weights</li><li class="equipment-single-item">Pastry brush</li></ul>
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Directions
<ol class="no-list-style"><li class="MethodStepper"><h4 class="step-title">Step 1</h4>Begin the fermentation process 3 days before serving. In a medium saucepan, warm 150ml of the cream and all the milk to 65°C. Remove from heat, add the koji rice, stir well, and let cool to room temperature. Transfer to a clean ceramic or glass container, cover with a breathable cloth, and ferment at room temperature (20-22°C) for 48-72 hours. The mixture will thicken and develop a pleasantly tangy, umami aroma. The enzymatic activity in koji breaks down proteins and starches into amino acids and sugars, creating complex flavor compounds.</li><li class="MethodStepper"><h4 class="step-title">Step 2</h4>For the charcoal pastry shell, combine the plain flour, almond flour, activated charcoal powder, and salt in a food processor. Pulse to mix. Add the cold butter cubes and pulse until the mixture resembles fine breadcrumbs. Add the icing sugar and pulse briefly. Add the egg and process just until the dough comes together. The minimal processing prevents gluten development, ensuring a tender, crisp tart shell.</li><li class="MethodStepper"><h4 class="step-title">Step 3</h4>Turn the dough onto a lightly floured surface, shape into a disk, wrap in cling film, and refrigerate for at least 1 hour. Cold dough is essential for maintaining the butter's solid state, which creates steam during baking and results in flaky layers.</li><li class="MethodStepper"><h4 class="step-title">Step 4</h4>Preheat your oven to 180°C. Roll the chilled dough to 3mm thickness and line your tart tins, pressing gently into the corners. Trim the excess and prick the bases with a fork. Return to the refrigerator for 20 minutes to rest and chill – this prevents shrinkage during baking.</li><li class="MethodStepper"><h4 class="step-title">Step 5</h4>Line each tart shell with parchment paper and fill with baking beans. Blind bake for 15 minutes, then remove the beans and paper and bake for another 5-7 minutes until the shells are dry and set. The charcoal not only provides color but also absorbs some of the butter's moisture, helping to maintain crispness. Allow to cool completely.</li><li class="MethodStepper"><h4 class="step-title">Step 6</h4>When the koji mixture has properly fermented, strain it through a fine-mesh sieve, pressing gently to extract all liquid. Discard the solids. You should have approximately one cup of fermented milk-cream mixture with a slightly thickened consistency.</li><li class="MethodStepper"><h4 class="step-title">Step 7</h4>Preheat the oven to 150°C. In a saucepan, combine the fermented mixture with the remaining 150ml cream, maple syrup, vanilla seeds and pod. Heat until it just starts to simmer around the edges, then remove from heat and let steep for 10 minutes to infuse the vanilla.</li><li class="MethodStepper"><h4 class="step-title">Step 8</h4>In a bowl, whisk the egg yolks with the caster sugar until pale but not foamy – excessive air bubbles would disrupt the smooth texture of the custard. Remove the vanilla pod from the cream mixture and gradually whisk the warm cream into the egg mixture, being careful not to create air bubbles.</li><li class="MethodStepper"><h4 class="step-title">Step 9</h4>Strain the custard mixture through a fine-mesh sieve to remove any lumps or remaining solids. The strain is crucial for achieving the silkiest possible texture. Pour the custard into the cooled tart shells, filling them about 85% full.</li><li class="MethodStepper"><h4 class="step-title">Step 10</h4>Carefully transfer the filled tarts to the oven and bake for 15-18 minutes, or until the edges are set but the center still has a slight wobble when gently shaken. The target internal temperature is 75-77°C – at this temperature, the proteins in the egg yolks coagulate perfectly without becoming rubbery.</li><li class="MethodStepper"><h4 class="step-title">Step 11</h4>Allow the tarts to cool at room temperature for 30 minutes, then refrigerate for at least 2 hours to completely set the custard. Just before serving, brush the tops lightly with maple syrup for a subtle sheen. If using, dust the edges of the tart shells sparingly with edible gold dust for an elegant contrast against the black charcoal.</li><li class="MethodStepper"><h4 class="step-title">Step 12</h4>Serve chilled but allow to sit at room temperature for 15 minutes before eating to allow the complex koji flavors to fully express themselves. The contrast between the earthy black shell and the golden custard with its umami notes creates a truly memorable dessert experience.</li></ol>
Chef’s Notes
A few helpful details for making this recipe.
What is koji and why is it used in desserts?
Koji is a Japanese culturing agent made from rice inoculated with Aspergillus oryzae mould. In desserts, it adds complex umami flavours, breaks down proteins into amino acids, and creates natural sweetness through enzymatic activity. It brings surprising depth and savoury notes that beautifully balance sweetness.
How can I achieve the perfect custard texture without curdling?
For perfect custard, heat to precisely 75-77°C using a digital thermometer, strain thoroughly before baking, avoid creating air bubbles when mixing, bake until just set with a slight wobble in the centre, and cool gradually. The tarts should be removed from the oven when still slightly jiggly in the middle.
Can I make a charcoal dessert shell without compromising taste?
Absolutely! Food-grade activated charcoal adds dramatic colour without affecting flavour when used in small amounts (5g per recipe). It actually helps crisp the pastry by absorbing moisture. Ensure you're using food-grade charcoal, not the barbecue variety, and pair with flavourful fillings that shine against the black backdrop.
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