Preheat oven to 350°F (180°C). Spray 2 (9-inch) round cake pans with baking spray with flour.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter, sugar, and lemon zest at medium speed until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs, one at a time, beating well after each addition. Beat in vanilla.
In a medium bowl, whisk together 3 cups (375 grams) flour, baking powder, and salt. With mixer on low speed, gradually add flour mixture to butter mixture alternately with crème fraîche, beginning and ending with flour mixture, beating just until combined after each addition.
In a small bowl, toss together blueberries and remaining 2 tablespoons (14 grams) flour until well coated.
Transfer half of batter (about 710 grams) to a large bowl; fold in ¾ cup (105 grams) blueberries. Fold ¾ cup (105 grams) blueberries into remaining batter in mixer bowl. Pour into prepared pans, smoothing tops with an offset spatula. Top with remaining ½ cup (70 grams) blueberries (¼ cup or 35 grams each).
Bake until a wooden pick inserted in center comes out clean, 30 to 35 minutes. Let cool in pans for 10 minutes. Remove from pans, and let cool completely on wire racks.
Level cooled cake layers, if desired. Place 1 cake layer on a serving plate. Spread 2 cups (373 grams) Crème Fraîche Buttercream on cake layer, and top with remaining cake layer.
Transfer 1 cup (187 grams) Crème Fraîche Buttercream to a pastry bag fitted with a French star piping tip (Ateco #865). Spread remaining buttercream on top and sides of cake. Pipe buttercream around top edges of cake as desired; garnish with blueberries, if desired. Cover and refrigerate for up to 3 days.