1-Start by preheating your oven to 325°F (163°C) and prepare three 8-inch cake pans with grease or liners for easy release. Mix the graham cracker crumbs, melted butter, sugar, and salt in a bowl, then press this mixture firmly into the bottom of each pan and bake for 4 minutes to set the base.

2-For the cake batter, whisk the dry ingredients cake flour, baking powder, and salt together in one bowl, and in another, combine the wet ingredients like buttermilk, sour cream, key lime juice, vanilla extract, and key lime zest.

3-Next, beat the sugar and canola oil together until well blended, then add the eggs one at a time, mixing after each. Alternate adding the dry and wet mixtures to the batter, stirring just until combined to keep the cake tender remember, overmixing can make it tough. Pour the batter over the pre-baked crust layers and bake for 28 to 34 minutes, or until a toothpick comes out clean.

4-For the key lime curd, cook the egg yolks, whole eggs, and sugar over low heat in a saucepan until thickened, then stir in the key lime juice, zest, and butter until smooth, and chill it until set. To make the vanilla bean buttercream, beat the unsalted butter until creamy, gradually add powdered sugar, vanilla bean paste, salt, and heavy cream, whipping until it’s light and fluffy. Assemble the cake by layering each piece with buttercream and lime curd, apply a crumb coat, chill to firm up, then finish with a smooth layer of buttercream for that professional look.