Step 1

Center a rack in the oven and preheat the oven to 350F.

Step 2

Butter an 8 inch square pan and put it on a baking sheet.

Step 3

For the Crumb:

Step 4

Put all the ingredients except the nuts in a food processor and pulse just until the mixture forms clumps and curd and holds together when pressed.

Step 5

Scrape the topping into a bowl, stir r the nits and press a piece of plastic against the surface. Refrigerate until needed.

Step 6

For the Bananas:

Step 7

Combine the butter and sugar in a flambe pan or skillet.

Step 8

Place the pan over low heat either on an alcohol burner or on top of the stove, and cook, stirring, until the sugar dissolves.

Step 9

Stir in the banana liqueur, then place the bananas in the pan.(if not using liqueur, just add bananas)

Step 10

When the banana slices soften and begin to brown, carefully add the rum. (again, if not using rum, simply take bananas out at this time)

Step 11

Continue to cook the sauce until the rum is hot, then tip the pan slightly to ignite the rum.

Step 12

When the flames subside, lift the bananas out of the pan and place aside to cool until needed.

Step 13

To make the cake:

Step 14

Whisk together the flour, baking powder, baking soda, salt, cinnamon and nutmeg.

Step 15

Add the butter and, with the paddle or whisk attachment, or with a hand mixer, beat the sugar with the butter at medium speed until light, about 3 minutes.

Step 16

Add the eggs one by one, beat for about 1 minute after each addition, then beat in the vanilla extract. Don't be concerned if the batter looks curdled-it will soon smooth out.

Step 17

Reduce the mixer speed to low and add the flour mixture and the buttermilk alternately, the flour in 3 parts and the buttermilk in 2 (begin with the dry ingredients).

Step 18

You will have a thick, cream batter.

Step 19

Add the banana fosters mixture and mix on medium speed for about 30 seconds. You don't really want chunks of bananas, you want them integrated like you would in  banana bread.

Step 20

Scrape the batter into the buttered pan and smooth the top gently with the spatula.

Step 21

Pull the crumb mix from the refrigerator and, with your fingertips, break it into pieces. There's no need to try to get even pieces-these are crumbs, they're supposed to be lumpy and bumpy and every shape and size.

Step 22

Scatter the crumbs over the batter, pressing them down ever so slightly.

Step 23

Bake for 55 to 65 minutes, or until the crumbs are golden and thin knife inserted into the center of the cake comes out clean.

Step 24

Transfer the cake to a rack and cool just until it is warm or until it reaches room temperature.

Step 25

Pour caramel sauce over the top if desired.