Preheat the oven to 350. Line the bottom of the pan with parchment rounds and lightly grease the sides of the pan with coconut oil using a pastry brush. If you don't have parchment rounds, lightly grease the bottom of the plan as well.
First, mix the milk and apple cider vinegar in a measuring cup to create a buttermilk, then set aside.
Then cream ½ cup butter and half the sugar with a paddle attachment in a stand mixer until light and fluffy - about 1 minute. Then, add the other half of the sugar and the oil and mix for another minute until fluffy.
Add the vanilla bean paste and two eggs and mix for 20 seconds. Then, add the other two eggs, scrape the bottom of the mixer with a rubber spatula, and mix for another 20 seconds.
Whisk the flour, cornstarch, baking powder, baking soda, and salt in a medium bowl.
Pour half of the dry ingredients into the wet ingredients and mix on low until almost combined, then on medium until fully combined. Add the milk mixture and the remaining dry ingredients and mix for 90 seconds until there are no clumps.
Divide the batter evenly between the 2 cake pans and bake for 33 to 38 minutes until a toothpick inserted into the center comes out clean. I like to weigh these on a food scale to ensure both pans will bake evenly.
Cool the cakes in their pans on a wire rack for 15 minutes. Then, run a knife along the edge of the pans, place a wire rack over the top of the pan, and gently turn out the cakes. Cool the cakes completely.
Buttercream directionsWhip 1 cup of butter in a stand mixer until light and creamy - about 2 minutes.
Add the vanilla extract, powdered sugar, salt, 3 tablespoons of heavy cream, 18 drops of blue food coloing, and 6 drops of yellow food coloring and mix on low until incorporated. Increase the speed to medium-high and mix until the frosting is smooth and creamy.
If the frosting is too thick, add another tablespoon of cream to thin it out.
Add a layer of frosting to the top of one of the cooled cake rounds. Then, add the other cake round on top and frost the entire outside and top. Add frosting dollops on top of the cake if desired and decorate with edible flowers.
Video
Notes
Storage
Store for up to 4 days at room temperature in an airtight container.
Refrigerate for up to a week in an airtight container.
Flash freeze a whole cake, wrap it in a double layer of plastic wrap and a layer of foil, and freeze for up to 3 months.
Wrap individual slices in plastic wrap and freeze for up to 3 months in an airtight, freezer-safe container.
Defrost overnight in the refrigerator.
Tips
If you don't have a food scale, loosely spoon the flour into your measuring cup and level it off with a knife to avoid compacting.
If the cakes are too rounded to easily stack, use a sharp, serrated knife to trip them flat.
Mix your cake batter until just combined. Overmixing can make the cakes tough.