Preheat oven to 375 degrees and butter an eight-inch round baking pan.
If using a bar of chocolate, chop into small pieces. In a double boiler over barely simmering water, melt chocolate with butter, stirring until smooth. Remove from heat and whisk sugar into chocolate mixture. Add eggs and whisk well.
Sift 1/3 cup sifted Squash Powder into melted chocolate mixture and stir to combine. Pour batter into pan and bake in the middle of the oven for 25 minutes, or until top has formed a thin crust. Cool for five minutes.
Dust cake with additional cocoa powder if you’d like a stronger chocolate flavor. (The cake will have the thickness of brownies).