These incredibly easy-to-make cake bars get a touch of sparkle and crunch from a sprinkle of turbinado sugar over the top. If you use frozen berries, thaw and pat them dry before topping the batter with them.
Preheat oven to 350 degrees F. Coat a 9-inch-square baking pan with 2 teaspoons butter.
Beat the remaining 4 tablespoons butter, granulated sugar and oil in a stand mixer fitted with a paddle attachment, or with a hand mixer, until light and fluffy, about 2 minutes. Beat in egg and vanilla until smooth.
Whisk flour, baking powder and salt in a medium bowl. Add the dry ingredients to the wet ingredients and mix until halfway combined. Add milk and mix just until combined. Do not overmix.
Spread the batter in the prepared pan. Sprinkle blackberries and blueberries over the top and lightly press them into the batter. Sprinkle with almonds and turbinado sugar.
Bake until puffed and golden and a toothpick inserted into the center comes out clean, 40 to 45 minutes.
Let cool slightly, then cut into 9 squares.