Use three greased 8-inch pans with parchment circles on the bottoms, and heat the oven to 350°F. Whisk the salt and leaveners through 3 cups of cake flour. Mix the 1/3 cup lemon juice into the buttermilk in a separate container.

Beat 1 cup butter with sugar and zest for 2–3 minutes. Add vanilla and eggs one at a time. Mix in dry ingredients in three additions, alternating with the liquid in two additions, just until smooth.

Toss fresh blueberries with the separate 2 teaspoons flour and fold gently into batter. Divide among pans. Bake 25–30 minutes, or until the centers are set and a tester has no wet batter. Cool fully before removing and stacking.

For the layer frosting, beat 3/4 cup butter with 12 ounces cream cheese and 1 1/2 teaspoons lemon juice. Gradually add 4 1/2 cups powdered sugar, then more up to 5 1/2 cups as needed. Use 1–2 tablespoons cream only to loosen overly thick frosting.

Stack the cooled layers with about 3/4 cup frosting between each. Apply a thin crumb coat, refrigerate 30 minutes, then spread the remaining frosting over the outside. Cut into 12 slices. Allow at least an hour for cooling before the crumb-coat chill.