In a small saucepan, pour in 150 g of heavy cream. Add the egg yolk and sugar. Stir gently with a silicone spatula over low heat until the sugar dissolves and the mixture becomes smooth.

When small bubbles begin to form around the edges (without boiling), add the dark chocolate. Stir until completely melted and silky smooth. If the texture looks grainy, strain it for a finer consistency. Let the mixture cool slightly, then transfer to a piping bag.

Pipe the chocolate filling into each tart shell, filling them about 80% full to leave space for toppings. Place the filled tarts in the refrigerator for at least 4 hours to allow the filling to fully set and firm up.

(If you're skipping the topping, your chocolate tartlets are ready to enjoy at this point!)

In a mixing bowl, combine 100 g of heavy cream and 5 g of sugar. Whip with an electric mixer on medium speed until soft peaks form — it should thicken but still flow slightly.

Add the chocolate sauce and continue whipping at medium-high speed until stiff peaks form. The cream should hold its shape when the whisk is lifted. Transfer the whipped cream into a piping bag with your favorite nozzle.

Once the tartlets are fully chilled and the filling is firm, pipe the chocolate whipped cream on top. Swirls, domes, or rosettes all look stunning. Finish with chocolate shavings or chips for a touch of elegance and crunch. Serve immediately or store chilled until ready to enjoy.