Preheat your oven to 350°F (175°C) and grease and flour two 6- or 7-inch round cake pans.

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

Blend ground pistachios with granulated sugar in a food processor until it reaches a fine texture.

Whisk together all-purpose flour, baking powder, salt, and the pistachio-sugar mixture in a large mixing bowl until combined.

In a separate bowl, whisk together the prepared buttermilk, olive oil, vanilla extract, and almond extract.

Gently fold the dry ingredients into the wet mixture until just combined, being careful not to overmix.

Divide the batter evenly between the two prepared cake pans and bake for 25-30 minutes.

Allow the cakes to cool for about 10 minutes in the pans before transferring to a wire rack to cool completely.

Beat softened butter until smooth and creamy, then gradually mix in blackberry preserves and powdered sugar.

Once cooled, level the tops of the cakes if necessary, layer frosting and blackberry preserves between the cakes.

Decorate the top with fresh blackberries and chopped pistachios before serving.