Combine all of the ingredients in a bowl and stir until smooth.
FOR THE CAKE
Preheat your oven to 325 degrees F. Prep your pan goop by mixing the flour and the softened butter in a small bowl until combined. With a pastry brush, brush the sides and all cracks and crevices of the pan with the goop. Set aside.
In a medium sized saucepan, cook the blueberries over medium-low heat until the berries soften. Transfer berries to a blender and pulse until smooth. After you puree, you should have at least one cup of purred berries. Set aside.
In a medium bowl, whisk together the cake flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream the butter and sugar together on medium-high for about 3-4 minutes, until lighter in color.
With the mixer on medium speed, add the egg whites and whole eggs, one at a time, mixing well after each addition (about 30 seconds). Make sure to scrape down the sides and bottom of the bowl between additions. Once all of the eggs are added, turn the mixer to medium-high and beat for an additional minute.
With the mixer on low, stir in the vanilla extract and blueberry emulsion.
Alternately add the dry ingredients with the blueberry puree in two additions, starting with the dry ingredients.
NOTE: To get a nice blueberry blue, I added navy blue AmeriColor food gel. You can totally just leave it the way it is, or add the extra food coloring.
Pour the cake batter into the prepared bundt pan and bake for 50 to 60 minutes or until a toothpick inserted in the center of the cake comes out with only a few moist crumbs on it.
Allow the cake to cool in the bundt pan completely before transferring it out of the bundt pan and onto a plate for serving.