Preheat your oven to 350°F and prepare a 9-inch round cake pan with parchment paper and a light butter coating. Cream together the softened butter and sugar until it's pale and fluffy, which takes about 3 minutes with an electric mixer. You'll know it's ready when it looks almost white and holds peaks when you lift the beaters.

Add eggs one at a time, beating well after each addition so the batter stays smooth and airy. Scrape down the bowl between additions—don't skip this step or you'll have pockets of unmixed butter hiding in the batter. Split your vanilla bean lengthwise and scrape out the tiny seeds, then stir them into the mixture for that beautiful speckled look.

In a separate bowl, whisk together flour, baking powder, and salt until fully combined and no lumps remain. Alternate adding dry ingredients and milk to the butter mixture in three additions, starting and ending with the dry ingredients. This method keeps the batter light and prevents overmixing, which would make your cake dense and tough.

Pour batter into the prepared pan and smooth the top with a spatula, then bake for 35 to 40 minutes until a toothpick inserted in the center comes out clean. Don't open the oven door during the first 30 minutes or you'll mess with the rise. Once it's golden on top and springs back when you gently touch it, pull it out and let it cool in the pan for 10 minutes.

Turn the cake out onto a wire rack and cool completely—I know it's tempting to slice into warm cake, but trust me, it'll crumble if you don't wait. Once cooled, cut the cake into bite-sized cubes about 1 inch square. You want pieces small enough that you get cake in every spoonful but big enough that they hold their shape.

Whip the heavy cream with powdered sugar and vanilla extract until it forms stiff peaks—this takes about 2 to 3 minutes depending on your mixer. Be careful not to overbeat or you'll accidentally make butter, and yes, I've done this more times than I'd like to admit. The cream should be thick enough to hold a shape but still soft and cloud-like.

Wash and dry your strawberries and blueberries, then gently toss them in a small bowl with 1 tablespoon of sugar to bring out their natural juices. In a large glass trifle bowl, layer one-third of the cake cubes on the bottom, breaking pieces to fit snugly. Top with half the whipped cream, then layer half the strawberries, then half the blueberries.

Repeat the layers: remaining cake cubes, remaining whipped cream, remaining strawberries, and remaining blueberries on top for that gorgeous red white blue trifle cozy presentation. Cover loosely with plastic wrap and refrigerate for at least 30 minutes so the flavors meld together. The trifle actually tastes better if you make it a few hours ahead, and the cool temperature makes it extra refreshing on a warm summer day.