3 1/2 tbsp. bitter cocoa powder
1 c. confectioners sugar
5 egg whites
2/3 c. granulated sugar

For the mousse: 6 1/2 tbsp. butter 3 egg yolks 4 egg whites 5 tsp. granulated sugar

Preheat the oven to 300 degrees. Butter and lightly flour the baking sheet or cover the baking sheet with parchment paper. Mix the cocoa powder with the confectioners sugar and sift together. Beat the egg whites until firm (about 3 minutes) adding 1 1/2 tablespoons sugar halfway through. As soon as the egg whites are stiff, add the remaining sugar at low speed, then with the wooden spatula, quickly fold in the cocoa-sugar mixture.

Draw three 9-inch rounds on the baking sheet to guide you when making the meringues. Take the pastry bag with 1/2-inch nozzle, fill it with chocolate meringue, and make three rounds by squeezing out the meringue in a spiral.

Bake in a 300 degree oven for 1 hour. Check the color of the meringue after 15 minutes of baking. The meringues should not brown. If they do, lower the heat of the oven. The meringue strips will be done first and should be removed while the large ovals might need 10 minutes extra baking. When they are cooked, the meringues are hard and can easily be detached from the baking sheet. While the meringue is baking, prepare the chocolate mousse as follows:

Melt the chocolate in a double boiler. Remove from the heat and add the butter, stirring it in with a wooden spoon. Allow the mixture to cool completely. It should be the consistency of a very thick cream. Then stir in the egg yolks one by one.

Beat the egg whites until very stiff; halfway through, add the sugar. Fold the chocolate mixture into the egg whites with the wooden spatula, making sure the two elements are perfectly blended together.