Rich Chocolate Éclairs for a French Pastry Night

Weigh everything in separate ramekins—choux waits for no one once it starts. Fit a large piping bag with a 1.5 cm (½-inch) French star tip; the fluted edge maximizes surface area and looks professional. Preheat oven to 220 °C / 425 °F (not convection yet). Trace twelve 10 cm × 2 cm rectangles on parchment, flipping the paper so ink doesn’t bake into shells.

In a medium saucepan combine 120 g unsalted butter, 240 ml whole milk, 120 ml water, 6 g sugar, and 3 g salt. Bring just to a boil; butter should be melted but milk not scorched. Off heat, dump in 140 g bread flour + 10 g cornstarch all at once. Stir with a wooden spoon until a film forms on the pan bottom (about 90 s). You’ve gelatinized starch; this pre-swelling prevents collapse later.

Transfer roux to a stand-mixer bowl. Paddle on medium for 3 min to drop to 60 °C / 140 °F. Crack 4 large eggs into a jug. With mixer on medium, add eggs in four additions, letting each absorb before the next. You may need ½ extra beaten egg; aim for the famous “V” that forms when you lift paddle and batter ribbons, folding slowly back onto itself.

Pipe batter onto traced lines, holding bag at 45° and letting the weight of dough drag tip along paper. Smooth peaks with a damp fingertip. Slide into lower third of oven, immediately spritz walls with water, and close door to create steam. Bake 10 min, then drop temperature to 190 °C / 375 °F, bake 20 min more. Do NOT open door early or shells deflate. They’re done when golden, firm, and feel hollow underneath.

Remove trays, poke a small hole in each end with a toothpick to vent, then return to switched-off oven with door ajar for 15 min. This step dries centers so they stay crisp once filled.

Whisk 500 ml milk, 100 g sugar, 40 g Dutch cocoa, 1 scraped vanilla bean, ½ tsp espresso powder, and 5 egg yolks in a saucepan. Cook over medium, stirring constantly, until it thickly coats spatula (82 °C / 180 °F). Off heat, stir in 30 g butter and 100 g chopped bittersweet chocolate until glossy. Strain through fine sieve to remove any curdled bits, press plastic wrap directly onto surface, chill 2 h.

Once cold, beat custard 10 s to loosen. In separate bowl whip 200 ml cold cream to soft peaks; fold into custard for a mousse-like filling that won’t ooze when sliced.

Transfer custard to piping bag fitted with Bismarck tip. Insert tip into one end of each shell, squeeze until you feel slight resistance. You’ll use about 45 g filling per éclair. Wipe away any excess.

Heat 120 ml heavy cream to just steaming, pour over 150 g chopped dark chocolate (60 %), let stand 2 min, then whisk smooth. Add 15 g corn syrup for shine and 15 g butter for elasticity. Cool to 30 °C / 86 °F—this is crucial; too hot and it slides off, too cool and it sets dull. Dip tops of filled éclairs, tilting to allow excess to drip back. Garnish with chocolate shavings or gold leaf if you’re feeling Parisian.

Refrigerate finished éclairs 30 min to set glaze, then serve at cool room temperature. They’re at their peak for 6 h; after that the shell gradually softens—still delicious, but less shatter.