Preheat oven to 350, then spray a 9" round cake pan with baking spray with flour.
Beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape the sides of the bowl.
Add eggs, one at a time, beating well after each addition, then beat in almond extract.
In a bowl, whisk together flour, baking powder and salt.
Reduce mixer speed to low, then gradually add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition.
Fold in ⅔ cup almonds.
Pour ¼ cup melted butter into the prepared pan, then sprinkle with ¾ cup brown sugar.
Arrange enough blackberries in a single layer over brown sugar to completely cover the bottom of the pan.
Pour batter over blackberries, smoothing the top with a spatula.
Bake until a wooden pick inserted in the center comes out clean, 40 to 45 minutes.
Let cool in the pan for 10 minutes.
Run a knife around the edges of the pan to release the sides of the cake, then carefully flip over onto a plate.
In a bowl, stir together the remaining ¼ cup melted butter, remaining ½ cup brown sugar, and remaining ⅔ cup almonds.
Sprinkle over top of cake, then top with remaining blackberries.
Serve warm or at room temperature. Enjoy!