Lightly oil a 6-inch springform pan, cake pan, or casserole, and sprinkle evenly with sugar. Preheat the oven to 350F
In a small bowl, melt butter, oil and chocolate together using a low microwave setting, or by placing the bowl over a pan of just-simmering water. Stir to combine.
Add 1 Tbsp sugar, cocoa powder,vanilla, and salt stirring to cool. Stir in 2 egg yolks and one whole egg.
In a clean dry bowl, beat 2 egg whites until foamy. Add 1/4 cup sugar, 1 Tbsp at a time, and continue beating until meringue is stiff and glossy.
Fold 1/3 of meringue into chocolate batter to lighten it. Then add remaining meringue, folding gently to maintain volume.
Turn batter into prepared pan. Bake at 350F until nicely puffed and just firm. Baking time will vary with accuracy of oven temperature and size of pan. Start checking for doneness at the 20 minute mark.
Cool cake in the pan on a wire rack. The cake will fall — it’s not a mistake. Cool to room temperature before removing springform pan collar. Do not attempt to turn the cake out of a standard pan — it is too soft. Do not refrigerate before serving. Leftovers may be refrigerated, but return to room temperature for best texture.
Fill with whipped cream and decorate with fruit. Berry coulis, caramel sauce, or chocolate sauce add a nice touch.