Preheat your oven to 350°F (175°C) and prepare two 6- or 7-inch round cake pans by greasing with olive oil and dusting with flour.

In a small bowl, combine your chosen milk with apple cider vinegar or lemon juice and let it sit for about 5 minutes.

In a food processor, pulse the ground pistachios and sugar until finely ground but still textured. Set aside.

In a large mixing bowl, whisk together the pistachio mixture, all-purpose flour, baking powder, and salt.

In another bowl, whisk together the buttermilk, olive oil, vanilla extract, and almond extract.

Fold the dry ingredient mixture into the wet mixture using a spatula until just combined.

Divide the batter evenly between the prepared pans and bake for 25 to 30 minutes until a toothpick inserted comes out clean.

Let the cakes cool in the pans for 10 minutes before transferring to a wire rack. Wrap in plastic wrap and refrigerate overnight.

Beat the softened butter in a mixing bowl until creamy, then gradually add blackberry preserves and powdered sugar, beating until fluffy.

Once cool, level the cakes and frost the top of one layer with buttercream and blackberry preserves before placing the second layer on top.

Frost the top and sides of the cake, then decorate with fresh blackberries and chopped pistachios.