Bursting Blueberry Lemon Layer Cake.

1. Preheat oven to 350 degrees F. Grease 3 (8-inch) round cake pans. Line with parchment paper, then butter/spray with cooking spray.2. In the bowl of a stand mixer (or use a hand-held mixer) beat together the coconut oil, yogurt, eggs, sugar, brown sugar, vanilla, buttermilk, lemon juice, and zest. Add 3 3/4 cups flour, baking powder, baking soda, and salt. Mix until just combined. 3. Toss the blueberries with the remaining 1 tablespoon flour and fold them into the batter. Swirl in the blueberry jam, leaving a few streaks of jam throughout the batter, it shouldn't be fully incorporated.4. Pour the batter among the 3 cake pans and bake 30-35 minutes, until the tops are just set and no longer wiggly in the center. Remove and let cool five minutes, then run a knife around the edges of the pan and turn the cakes out onto a cooling rack. Cover and let the cakes cool completely before assembling.5. To make the buttercream. Add the butter, mascarpone, and powdered sugar to the bowl of a stand mixer. Beat the butter and powdered sugar together until the butter is light and fluffy. Divide the buttercream between 3 bowls. Mix 1-2 tablespoon jam into 1st bowl, then 2-3 tablespoons jam to the 2nd bowl. Leave the 3rd bowl plain. 6. To assemble, place one cake layer on a serving plate or cake stand. Spread the darkest colored buttercream over the cake. Add the 2nd cake layer and spread with the lighter colored buttercream. Add the final cake layer and spread with the white buttercream. Lightly frost the outside of the cake, swirling the different shades together. It's shouldn't look "perfect". Chill 30 minutes. Serve, or store in the fridge for up to 3 days.