Preheat oven to 350F. Sift flour, ½ cup sugar, and peanut butter powder into a medium bowl.
Combine egg whites, salt, and cream of tartar in a mixer bowl. Using the whisk attachment, beat mixture on medium-high until firm peaks form.
Reduce mixer to medium and gradually add remaining sugar (1 ¼ cups). Beat on high speed until thick and shiny.
Add vanilla extract. Beat on high speed one more minute.
Sift ¼ of flour mixture into mixer bowl and carefully fold in, being cautious not to deflate the egg white mixture. Once fully combined, repeat with the remaining flour mixture in three more additions. Ensure that the mixture is completely combined, with no dry ingredients unmixed or white streaks.
Pour batter into an *ungreased* 10-inch tube pan, preferably an angel food cake pan with small feet (see notes). Smooth top of the batter.
Bake 30-35 minutes, or until top of cake springs back when touched. Invert pan on counter or cooling rack (see note), and allow to cool completely. Run a thin knife around the cake to remove it from the pan.
Ganache:
Place finely-chopped bittersweet chocolate in a medium heatproof bowl.
In a small saucepan, heat heavy cream and peanut butter until hot, but not boiling. You will start to see small bubbles around the edge of the pan when it's about ready.
Pour hot cream mixture over chocolate, making sure all the chocolate is covered. Let sit five minutes. Whisk until smooth. If not all chocolate is melted, you can place the ganache in the microwave on 15-second bursts until the mixture is smooth and glossy.
Pour ganache over cooled cake, allowing the ganache to drip down the sides.Enjoy!
Notes
Note on peanut butter powder: If you can't find it in your local grocery store, it is available [here].Note on pan prep: There is no need to grease the pan. Greasing the pan for an angel food cake will make it more difficult for the cake to rise in the pan, and your cake will likely collapse!Note on angel food cake pan: Angel food cakes are so light, they must be cooled upside down to prevent collapse after baking. Angel food cake pans have small feet on them that allow you to invert the pan (see [here]). If you do not have an angel food cake pan, invert the cake pan on a wire rack to cool.