Preheat oven to 220°C (425°F). Place 6 (or 8 small) 6-ounce (180 ml) ramekins on a baking sheet. Generously butter each ramekin and dust with a thin coating of flour, tapping out excess.

Melt chocolate and butter

Combine chopped dark chocolate and 170 g unsalted butter in a heatproof bowl set over a simmering pot of water (double boiler) or microwave in 20–30 second bursts, stirring between bursts, until completely melted and smooth. Remove from heat and let cool slightly (2–3 minutes).

Whisk eggs and sugar

In a separate large bowl, whisk together 4 large eggs and 1 cup granulated sugar vigorously until mixture is thickened, pale, and slightly increased in volume (about 2–3 minutes by hand or 1–2 minutes with an electric mixer on medium-high).

Combine chocolate with egg mixture

Temporarily temper the egg mixture by adding about one tablespoon of the warm melted chocolate into the eggs and whisk quickly, then fold in the remaining chocolate and butter mixture until homogeneous.

Add flavor and flour

Fold in 3 tablespoons Baileys Irish Cream, 1 teaspoon vanilla extract, 1 tablespoon all-purpose flour and a pinch of fine salt. Mix gently until fully incorporated — the batter should be glossy and fairly loose. Do not overmix.

Ramekins / finishing

Portion batter

Divide the batter evenly among the prepared ramekins (for 6 ramekins, fill about 3/4 full; for 8 smaller ones, fill accordingly). Smooth the tops with a spoon or offset spatula.

Bake

Bake on the middle rack for 10–12 minutes for molten centers (edges will be set and slightly risen, centers still soft). For more set centers, bake 13–14 minutes. Ovens vary, so check at 9 minutes onward.

Rest and unmold

Remove from oven and let rest 1 minute. Run a small knife around the inside edge of each ramekin to loosen. Place a plate on top of each ramekin, invert quickly, and lift the ramekin off. If the cake sticks slightly, tap gently or warm the ramekin briefly.

Finish and serve

Dust each petit gâteau lightly with powdered sugar. Serve immediately with a scoop of vanilla ice cream or a dollop of mascarpone and garnish with fresh raspberries or mint if desired.