1-Step: Prep the pan and oven Preheat your oven to 350°F (175°C). Prepare a 9-inch square pan with parchment paper, or grease and flour it well. This helps the cake release cleanly later, which matters when you want neat slices of blueberry mousse cake.

2-Step: Mix the cake batter In a large bowl, cream together 1/2 cup butter and 1 cup sugar until the mixture looks light and fluffy. Beat in the 2 eggs one at a time, then add 1 tsp vanilla extract. In a separate bowl, whisk together 1 1/2 cups cake flour, 1 tsp baking powder, 1/2 tsp baking soda, and 1/4 tsp salt. Add the dry ingredients to the butter mixture in parts, alternating with the 1/2 cup buttermilk. Mix just until combined. This keeps the cake tender and avoids overmixing, which can make a berry cake dense instead of soft.

3-Step: Bake the cake Spread the batter evenly in the prepared pan. Bake for 20 to 25 minutes, checking at the 20-minute mark. The cake is ready when a toothpick comes out with just a few moist crumbs. Cool the cake completely before adding the mousse.

4-Step: Make the blueberry mixture Puree 2 cups fresh blueberries. Place the puree in a saucepan with 1/2 cup granulated sugar and cook over medium heat for about 5 minutes, until slightly thickened. In a small bowl, bloom the 1 tbsp gelatin powder in 2 tbsp water, then stir it into the warm blueberry mixture until dissolved. After that, chill the blueberry mixture in the refrigerator for 1 to 2 hours, or until it is set but still soft. This step is important because the mixture needs to be cool before folding into the whipped cream.

5-Step: Whip the cream In a cold bowl, whip 1 1/2 cups heavy cream with 1/4 cup confectioners’ sugar and 1 tsp vanilla extract until stiff peaks form. The cream should hold its shape without looking grainy. This is what gives the mousse its airy texture.

6-Step: Fold the mousse together Once the blueberry mixture is cool and softly set, gently fold it into the whipped cream. Use a light hand so the mousse stays fluffy. Avoid stirring too hard, or you may lose the airy texture that makes a creamy blueberry mousse cake so pleasant to eat.

7-Step: Assemble the cake Line an 8-inch or 9-inch square pan with plastic wrap. Place the cooled cake inside, then spread the blueberry mousse evenly over the top. Smooth the surface with a spatula for a neat finish.

8-Step: Chill and slice Refrigerate the assembled cake for at least 4 hours, or overnight if you have time. This allows the mousse to set fully, so the slices hold together well. When ready to serve, lift the cake from the pan using the plastic wrap and garnish with fresh blueberries.

9-Step: Serve with a fresh finish Slice the cake with a clean knife for the best presentation. Wipe the knife between cuts if needed. Add extra berries right before serving for a bright, fresh look.