Preheat your oven to 350°F. Grease a 9-inch round cake pan and line the bottom with parchment paper—this prevents sticking and makes cleanup easier. Combine the flour, baking powder, and salt in a small bowl and whisk them together. Set aside for now.

In a large bowl, beat the 4 eggs and granulated sugar together until the mixture gets pale and fluffy, about 3 to 4 minutes. This is the step that gives your cake that airy texture. You'll know it's ready when it doubles in volume and looks creamy.

Gently fold the melted butter into the egg mixture using a spatula—don't overmix or you'll lose all that fluffy air you just created. Fold in the vanilla bean paste until combined, then carefully fold in the flour mixture in two additions, stirring just until no dry bits remain.

Pour the batter into your prepared pan and bake for 28 to 30 minutes, until a toothpick inserted in the center comes out with just a few moist crumbs. The top should be golden and springy to the touch. Let it cool in the pan for 10 minutes, then turn it out onto a wire rack.

While the cake cools completely (this takes about 30 minutes), make your whipped cream. Pour the heavy cream and powdered sugar into a chilled bowl and beat with an electric mixer on medium-high speed until stiff peaks form. Watch it closely after 2 minutes—don't walk away or you'll end up with butter.

Once everything's cooled, it's assembly time. Break or cut the cooled cake into bite-sized pieces—roughly 1-inch cubes work perfectly. Start layering in your trifle dish: cake pieces first, then a layer of whipped cream, then strawberries, then more cake, then whipped cream again, and finally top with blueberries for that gorgeous blue layer.

Chill your finished red white blue trifle for at least 15 minutes before serving so the layers set a bit. This actually makes serving cleaner and the flavors meld beautifully. You can assemble it up to 4 hours ahead, which is honestly my favorite part of this recipe.