Preheat oven to 325.
Add the butter and sugar to a bowl. Using a stand mixer, beat until well creamed. Add the egg and vanilla, beat until combined. Stir in the beer, and olive oil.
Sprinkle the flour, cocoa powder, baking soda, and salt. Stir until just combined.
Pour batter into a loaf pan that’s been greased and floured.
Bake for 60-65 minutes or until or until a cake tester inserted into the center of the loaf comes out with just a few crumbs.
Remove from oven and allow to cool completely.
In a blender add the blackberries, powdered sugar, lemon juice, and vanilla extract, blend until smooth.
Pour over the top of the cake, chill until set.
Remove from loaf pan and slice prior to serving.