Preheat your oven to 350°F (175°C) and prepare cake pans by greasing and flouring them.

Combine milk with apple cider vinegar or lemon juice and let sit for 5 minutes to thicken.

Pulse ground pistachios and sugar in a food processor, then mix with flour, baking powder, and salt.

Whisk together the milk mixture, olive oil, vanilla extract, and almond extract.

Fold the dry ingredients into the wet mixture until just combined, without overmixing.

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

Cool cakes in pans for 10 minutes, then transfer to a wire rack to cool completely.

Beat butter with blackberry preserves and gradually add powdered sugar, mixing until fluffy.

Level the top of one cake layer, spread buttercream and preserves, then place the second layer on top.

Frost the sides and top of the cake with remaining buttercream, then garnish with blackberries and chopped pistachios.