Chocolate mousse — a fluffy French dark chocolate dessert

Prepare six dessert cups or glasses holding about 180–200 ml, a metal bowl, a mixer and a spatula. Weigh the milk and cream in grams, not by volume. Leave the cream in the refrigerator and chill the bowl and beaters about 10 minutes. Meanwhile, prepare the chocolate base. Do not reserve chocolate or cream for garnish; the full amounts go into the mousse.

Chop all 200 g chocolate and put in a dry heatproof bowl. Set over a saucepan of gently steaming water so the bowl's base does not touch the water. Heat gently about 4–6 minutes, stirring until melted. Lift off the bowl and dry its underside. The water is only for heating; do not pour it into the chocolate and do not let condensation drip in.

Heat all 100 g milk in a small saucepan until the first tiny bubbles appear around the edge, then remove from the heat. Add to the chocolate in three portions, stirring in small movements from the center each time until smooth and glossy. Scrape all milk from the saucepan and chocolate from the bowl's sides. Do not add sugar, butter or more liquid.

Pour all 300 g cold cream into the chilled bowl. Beat on medium speed until thickened, forming a soft peak that bends over when the beaters are lifted. It should stay creamy, without butter lumps or a stiff dry texture. Do not sweeten. The chocolate base should stay warm and fluid meanwhile; do not refrigerate it and do not wait for it to set.

Check the base with a spatula: it should fall in a continuous smooth ribbon, still noticeably warm but no longer steaming. If it has begun to thicken, briefly warm the bowl over steam and stir again. Add about one-quarter of the whipped cream to the chocolate and mix a little more vigorously. This first portion loosens the heavier base so the rest can be incorporated without prolonged mixing.

Add the remaining whipped cream to the lightened chocolate in two portions. Each time, lift the spatula from the bottom upward and turn the bowl until pale streaks disappear. Scrape the bottom and edges too, but stop as soon as the color is even. Do not use the mixer again. The mousse is airy and quite soft; it reaches the right firmness only during chilling.

Divide all the mixture equally among six glasses, scraping both bowls thoroughly with a spatula. Do not pack down the mousse and do not bang the glasses on the worktop. Cover so the cover does not touch the surface and refrigerate immediately for at least 4 hours. You can make the dessert the previous evening. Do not freeze it instead of allowing the necessary chilling time.

Serve chilled, optionally taking the glasses from the refrigerator about 5 minutes beforehand for a fuller chocolate flavor. A spoonful should reveal a light even texture, without a liquid layer at the bottom. Do not add whipped cream, shavings or sauce. Keep remaining servings covered in the refrigerator and eat within 2 days of preparation; take out only the glasses you are about to serve.