Measure the topping ingredients into a medium bowl, and combine, using a large fork to kind of mash it all together. It will form nice big crumbles. Set aside.

Generously butter 4 small loaf pans and preheat the oven to 350º

In the bowl of a stand mixer, cream the butter.

Beat in the sugar and eggs, then the bananas and vanilla.

Combine the dry ingredients, and add to the butter mixture.

With the mixer running, add the buttermilk, and mix until completely combined and smooth – a minute or so at medium speed.

Fill the loaf pans about 1/3 full, in an even layer, reserving remaining batter for the moment.

Scatter a few tablespoons of the topping over the batter in each pan - you will use about half of the topping.

Divide the remaining batter among the pans, and smooth the top.

Scatter the remaining over the tops of the loaves, pressing lightly with the back of spoon to make sure it adheres to the cake.

Bake on the middle rack for about 35 to 40 minutes, turning the loaves and switching their relative positions about half way through. Test for doneness by inserting a toothpick near the center of the loaves - no more than a moist crumb or two should come out.

When done, cool in the pans for about 5 minutes, loosen the edges with a table knife, and finish cooling on a rack. Best served warm, and it can be reheated if wrapped in foil first.

Refrigerate leftovers.