Preheat the oven to 350°F (175°C) and grease two 6-inch round cake pans with olive oil or butter, dusting with flour.

In a medium bowl, mix 1 cup of milk with 1 tablespoon of apple cider vinegar or lemon juice and let sit for 5 minutes.

Pulse together ground pistachios and sugar in a food processor until finely blended.

Whisk together the pistachio-sugar mixture, flour, baking powder, and salt in a large bowl.

In another bowl, whisk the buttermilk mixture with olive oil, vanilla, and almond extracts.

Gently fold the wet ingredients into the dry ingredients until just combined.

Divide the batter between the two prepared cake pans and bake for 25-30 minutes, or until a toothpick comes out clean.

Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.

Beat together softened butter and blackberry preserves, then gradually add powdered sugar, mixing until fluffy.

Spread frosting between the cooled cake layers, and on top and sides of the cake, garnishing with fresh blackberries and chopped pistachios.