Preheat your oven to 350°F (175°C). Grease two 6- or 7-inch cake pans with olive oil or butter, then dust with flour.

Create a buttermilk substitute by combining one cup of milk with one tablespoon of apple cider vinegar or lemon juice and let it sit for about 5 minutes.

In a bowl, whisk together ground pistachios, all-purpose flour, baking powder, and salt until combined, then set aside.

In a larger bowl, mix the buttermilk substitute, olive oil, vanilla extract, and optional almond extract until smooth.

Gently fold the dry mixture into the wet ingredients until just combined; the batter should be slightly lumpy.

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

Let the cakes cool in pans for 10 minutes before turning out onto a wire rack to cool completely.

Make the frosting by beating together softened butter and blackberry preserves until smooth. Gradually add powdered sugar until fluffy, and mix in vanilla extract and thyme.

Level the first cake layer and spread frosting followed by a thin layer of blackberry preserves. Place the second layer on top and frost the cake.

Garnish the cake with fresh blackberries and chopped pistachios before serving.