Let’s break down this beautiful layer cake process:

Make the Cake:

1. Preheat & Prep Pans: Preheat oven to 350°F (177°C). Grease three 8-inch round cake pans, line with parchment rounds, then grease the parchment.
2. Cream Butter & Sugars: Using a mixer with a paddle attachment, beat the softened butter on high until smooth (about 1 min). Add granulated and brown sugars; beat on medium-high until combined (about 2 mins).
3. Add Oil, Eggs, Vanilla: Add the oil and beat until combined and creamy (about 3 mins). Add eggs one at a time, beating well after each, then beat in vanilla. Scrape bowl as needed.
4. Combine Dry Ingredients: In a separate large bowl, whisk together the 3 cups flour, baking powder, baking soda, and salt.
5. Alternate Wet & Dry: Add the dry ingredients to the wet ingredients alternately with the buttermilk and lemon juice (begin and end with dry). Beat on low speed just until combined after each addition.
6. Fold in Blueberries: Toss the fresh blueberries with 1 Tablespoon of flour. Gently fold the floured blueberries into the thick batter. Do not overmix.
7. Bake: Spoon batter evenly into the prepared cake pans. Bake for 22–26 minutes, or until a toothpick inserted in the center comes out clean.
8. Cool: Remove from oven, let cool in pans for about 10 minutes, then invert onto cooling racks to cool completely.

Make the Frosting:

1. Beat Cream Cheese & Butter: Using a mixer with the paddle attachment, beat softened cream cheese and softened butter together on medium speed until no lumps remain (about 3 full minutes).
2. Add Sugar & Liquids: Add confectioners’ sugar, heavy cream, vanilla extract, and salt with the mixer running on low.
3. Whip Frosting: Turn mixer up to high speed and beat for 3 minutes until light and fluffy.

Assemble and Frost:

1. Level Cakes: Using a large serrated knife, slice a thin layer off the tops of the cooled cakes to create flat surfaces.
2. First Layer: Place 1 layer on your cake stand or serving plate. Evenly cover the top with a generous layer of cream cheese frosting.
3. Second Layer: Top with the 2nd cake layer, add more frosting.
4. Third Layer & Crumb Coat: Top with the third layer. Use the remaining frosting to apply a thin “crumb coat” all over the cake, sealing in crumbs. The recipe notes it makes just enough for a light frost, so apply accordingly.
5. Chill: Refrigerate the cake for at least 45 minutes to set the crumb coat. This makes final frosting much easier.
6. Final Frost (Optional): If you made extra frosting or prefer a thicker layer, apply it now. Otherwise, the light frosting/naked look is intentional.
7. Garnish & Chill Again: Top with fresh blueberries or lemon zest/slices if desired. Refrigerate for at least 30-45 minutes before slicing to ensure stability.

Allowing the cake to chill is crucial before slicing!