Preheat oven to 350 degrees F. Line four 6-inch cake rounds with parchment paper. Lightly butter cake rounds and set aside.
In a small bowl, whisk together flour, baking powder, salt and blueberry powder. Set aside.
Cream together butter, sugar, and brown sugar in a stand mixer fitted with a paddle attachment. Add lemon zest. Add eggs one at a time and mix until fully incorporated.
In a measuring cup, combine buttermilk, blueberry puree, and vanilla paste.
Alternate adding flour mixture and buttermilk mixture into creamed butter. Mix until just incorporated. Scrape down bowl as needed to ensure thorough mixing.
Divide batter into prepared cake rounds. Level batter using a mini offset spatula or the back of spoon. Bake for 30-35 minutes until toothpick inserted in center of cake comes out clean.