Measure all the ingredients. In a bowl, combine the butter with the roughly chopped chocolate.

Melt the butter and chocolate together in a double boiler, stirring with a spatula until smooth and lump-free.

Separate the egg yolks and whites into two different bowls. Add 1/3 cup sugar (about 80 grams) from the total to the yolks and beat with an electric mixer until the mixture is pale and thick. While mixing, add the liqueur and the melted chocolate-butter mixture. Continue beating until well combined. At this point, add the grated orange zest.

Beat the egg whites until stiff peaks form, gradually adding the remaining sugar.

Gently fold the whipped egg whites into the almond and chocolate mixture, a little at a time, using slow, upward motions. Mix thoroughly, being careful not to deflate the batter.

Line a 11-inch (29 cm) sloped-edge aluminum cake pan with parchment paper. Pour in the batter and smooth the top. Bake in a preheated static oven at 350°F (180°C) for 20–25 minutes. Adjust baking time as needed for your oven and check with a toothpick. The cake should have a thin, delicate, crisp crust on the outside and remain soft, moist, and truffle-like inside.

Let the cake cool completely before transferring it to a serving plate, as it is very delicate and may break. Once fully cooled, dust with powdered sugar and serve. I used a small crocheted doily to create a pattern on top.