Preheat oven to 350° F. In the bowl of a food processor, pulse the sugar and freeze-dried blueberries (see note) until thoroughly combined. Set aside.
Sift flour and ½ cup blueberry sugar into a medium bowl. Set aside.
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 blueberry sugar. 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 with a spatula, 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 unmixed dry ingredients.
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.
For Whipped Cream
Pour cold heavy cream, powdered sugar, and vanilla bean paste (see note) in the bowl of a stand mixer fitted with the whisk attachment. Start the mixer on low speed, and gradually increase the speed to high. Whip until the cream thickens and forms peaks.
Serve the cake with the whipped cream and fresh blueberries, if desired.Enjoy!
Notes
Note on freeze-dried blueberries: Make sure to use *freeze-dried* blueberries, as they are free of moisture and will process into a powder along with the sugar. Note on cake flour: Cake flour is a must for this recipe! The texture of the cake won't be right (or could collapse completely) if you use another type of flour. Note on vanilla bean paste: It's no secret that I love vanilla bean paste. It's soooo tasty without the vanilla bean price tag (and it pretty much stays good forever). If you prefer to substitute, you can use 1 teaspoon vanilla extract. 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. If you do not have feet on your pan, invert the cake pan on a wire rack to cool.