Grease 2 8-inch round cake pans (OR 9X13 Baking pan baked for 16 min longer). Line with parchment and grease the parchment. Set aside.
Preheat oven to 180C/350F.
Brown the butter over medium heat until melted. Continue to cook until foaming subsides and the milk solids in the butter have turned browned. The butter will have a toasted caramel fragrance. Set aside to cool slightly.
Combined the cooled butter and sugars. Mix until creamed and smooth, 3 minutes.
Add eggs, one at a time and mix until incorporated.
Mix in vanilla, Rum, and mashed bananas.
Sift together the flour, baking powder, baking soda and salt.
Alternately add the dry ingredients with the soured goat milk, beginning and ending with the dry.
Divide batter evenly into prepared pans and bake in preheated oven until a skewer inserted in the middle comes out clean, 23-30 minutes.
Remove from oven and cool in pans for 5 minutes. Then invert onto cooling racks. While cooling, prepare frosting.
Boil butter, brown sugar and milk over medium heat for 2 minutes. Cool.
Sift in powdered sugar until you obtain the desired consistency.
Pour over cake and spread immediately.