In a bowl, mix 50 g of soft butter, 50 g of brown sugar, 50 g of flour, and 10 g of cocoa powder until a homogeneous dough forms.

Roll the dough thinly between two sheets of parchment paper.

Freeze for 30 minutes until firm but pliable. When ready to use, cut thin rings to top each piped cabbage.

Soak the gelatin leaves in cold water to soften.

Heat 500 ml of milk with half the sugar and a split vanilla bean (or vanilla extract) until just steaming.

Whisk the egg yolks with the remaining sugar and 40 g of cornstarch into a smooth, pale ribbon.

Temper the yolks by pouring hot milk over them while whisking steadily; then return the mixture to the saucepan and cook for 2–3 minutes until it thickens to a pudding consistency.

Off the heat, add 150 g of chopped dark chocolate and the drained, squeezed gelatin if using. Blend until silky and even.

Press plastic wrap directly on the surface and chill completely.

When fully cold, whip 200 ml of cold whole cream to firm peaks and fold gently into the cooled chocolate pastry cream to create the diplomat.

Preheat the oven to 200 °C.

In a saucepan, bring 125 g of water, 125 g of milk, 100 g of butter, a pinch of salt, and 1 teaspoon of sugar to a rolling boil.

Remove from heat and add 150 g of flour and 20 g of sifted cocoa powder all at once. Stir vigorously with a wooden spoon until the mixture forms a rough ball.

Return to medium heat for 1–2 minutes to evaporate excess moisture; the dough should feel slightly tacky but not wet.

Transfer to a mixing bowl and let sit for 5 minutes. Add the 4 eggs one at a time, fully incorporating each until the dough becomes glossy and forms a ribbon when lifted.

Fit a piping bag with a round tip and pipe uniform balls onto a baking sheet lined with parchment.

Remove the chilled cracker dough from the freezer, cut rings, and lay a ring atop each piped choux.

Bake at 200 °C for 20–25 minutes without opening the oven. If they need extra drying, lower to 180 °C for the last 5 minutes.

Cool completely on a wire rack; the shells should be hollow and dry inside, with the crackle on top echoing like a fine biscuit.

Using a serrated knife, cut the top of each cabbage or excavate a small hole at the bottom.

Fill a piping bag with the chocolate diplomat and pipe generously into each shell, building a small rose or mound of cream that spills slightly.

Place a small bar of dark chocolate into the cream before it sets so it nestles into the warm richness.

Chill until set and serve slightly cool.