Chocolate Yule Log

Cake:
Vegetable oil spray for greasing pan
200 grams granular sugar substitute
21.5 grams unsweetened cocoa powder
2 tablespoons Atkins Quick CuisineTM Bake Mix
9 large eggs, separated
1/4 teaspoon salt

Filling:
236 ml heavy cream
1 1/2 tablespoon granular sugar substitute

Frosting:
57 grams unsweetened chocolate, melted and cooled
79 milliliters heavy cream
1 stick (8 tablespoons) unsalted butter, softened
30 grams plus 1 tablespoon granular sugar substitute
1 tablespoon unsweetened cocoa powder
1/2 teaspoon vanilla extract