Grease the sides of each three 8-inch or 9-inch round cake pan with butter or nonstick spray.

Line the bottoms with parchment paper rounds to prevent sticking and ensure clean removal after baking.

Heat your oven to 350°F (175°C) so it’s ready when the batter is done.

In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter and granulated sugar together on medium speed until light, fluffy, and pale in color, about 3–5 minutes.

Stop halfway through to scrape down the sides and bottom of the bowl so everything mixes evenly.

In a medium mixing bowl, whisk together the eggs, egg whites, sour cream, milk, and vanilla extract until smooth and well combined.

In another medium bowl, whisk together the gluten free flour blend, potato starch, guar gum (if using), baking powder, baking soda, and salt.

This helps prevent clumps and ensures the leavening agents are evenly distributed.

Reduce the stand mixer speed to medium-low.

Add the dry and wet ingredients alternately to the butter-sugar mixture: begin with 1/3 of the wet, then 1/3 of the dry, repeating until all is incorporated, and ending with the wet mixture.

Gently toss the blueberries with 1 tablespoon of the dry flour mixture to coat them lightly (this prevents them from sinking).

Fold the blueberries into the batter with a spatula until evenly distributed.

Bake for 15 minutes, rotate the pans for even baking, then continue baking for another 15–20 minutes.

The cakes are done when the tops are golden brown and a toothpick inserted into the center comes out with only a few moist crumbs (no wet batter).

Remove pans from the oven and allow cakes to cool in the pans for about 15 minutes.

Peel off parchment paper and allow the cakes to cool completely before frosting.

In the bowl of a standing mixer fitted with the paddle attachment, beat the softened butter on medium speed for 2–3 minutes until it is light, creamy, and pale in color. This step helps develop a fluffy texture. You could also use an electric mixer / hand mixer and a large bowl.

Reduce mixer speed to low. Slowly add the sifted powdered sugar, 1 cup at a time, mixing after each addition. Scrape down the sides of the bowl as needed to ensure even mixing. Once all sugar is incorporated, beat on medium speed for 1 minute to fluff it up.

With the mixer on low, add the lemon juice and vanilla extract. Increase to medium speed and beat for 1–2 minutes until fully incorporated. The frosting should become slightly looser and take on a bright, citrusy aroma.

Add 1 tablespoon of heavy whipping cream and beat again on medium-high speed for 3-5 minutes. If the frosting seems too thick, add the second tablespoon of cream. If it’s too loose, add a little more sifted powdered sugar. Beat until smooth and airy.

To layer cake, place the first cake layer top side up, in the center of the cake board. Spread buttercream atop, then pipe a rim of the buttercream around the edge of the cake and fill the center with lemon curd.

Place the second cake layer on top of the buttercream and filling, bottom side down. Repeat piping and filling.

Place final cake layer, top side down (flip it so the flat bottom is facing up).

Place straws or popsicle sticks into the center of the cakes and three additional ones around the center, about 2 inches out.

Crumb coat the entire cake with a thin, even layer of the buttercream, covering the sides of the cake and the top of the cake in buttercream. Pop it into the freezer for about 10 to 15 minutes to set this layer of frosting.

Once the crumb coat is set, continue to frost the cake with the remaining frosting. I like to use a cake edger or scraper, but you don’t have to use this. You can always create a rustic look with a spatula.

Decorate the top of the cake however your heart desires!