Preheat oven to 350ºF.
If using slivered almonds, place into a food processor or coffee bean grinder. Pulse until finely ground; be careful not to over grind or it will turn to almond butter.
Combine finely ground almonds or almond flour, brown sugar and cocoa in a large mixing bowl.
In food processor or blender, purée beans and bananas until smooth.
Add eggs, oil and rum extract to beans and banana mixture. Mix well.
Add liquid mixture to dry ingredients. Mix until well blended.
Pour batter into a greased 8-inch round cake pan.
Bake for 30-40 minutes. After 30 minutes, check for doneness: toothpick inserted into center of cake should come out clean.
Cool in pan on a wire rack.