Preheat your oven to 400°F (200°C). On a baking sheet, mix the fresh blueberries with a drizzle of olive oil and some maple syrup. Roast for 10-15 minutes until they start to blister. Let cool.

Lower the oven temperature to 375°F (190°C) and grease two 9-inch round cake pans. In a bowl, whisk together flour, baking powder, lemon zest, and sea salt. In another bowl, beat butter and sugar until fluffy. Add eggs, olive oil, and lemon juice. Combine the dry ingredients with the buttermilk, folding in the roasted blueberries.

Divide the batter evenly between the prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for about 10 minutes before transferring them to a wire rack.

Mix together the blueberry preserves with a splash of lemon juice. This enhances the flavor for the filling.

Beat the softened butter until smooth. Gradually add powdered sugar and mix until well blended. Adjust the consistency with lemon juice and almond milk until it's spreadable.

Once the cakes are completely cooled, place one layer on a serving plate. Spread a layer of blueberry filling, followed by frosting. Top with the second cake layer and frost the top and sides. Chill briefly before serving.