1-First, preheat the oven to 350°F (175°C) and grease a 9×13-inch baking dish. This step sets the stage for even baking.

2-Next, in a bowl, crumble the cold butter cubes with flour, sugars, and cinnamon until the mixture resembles coarse crumbs; set it aside as your crumb topping.

3-Then, whisk together the dry ingredients: flour, baking powder, cinnamon, and salt in another bowl. For the wet ingredients, use a mixer to cream the softened butter for about 2 minutes, then add sugar and mix for another minute. Blend in the eggs, vanilla, and mashed bananas until everything is combined.

4-Alternately mix in the milk and dry ingredients on low speed until just incorporated, being careful not to overmix this keeps the cake light and fluffy. Spread half the batter in the prepared dish, sprinkle about a quarter to a third of the crumb topping over it, then add the remaining batter and cover with the rest of the topping. Bake for 50-55 minutes until a toothpick comes out clean, and let it cool before optionally whisking powdered sugar with milk for a glaze to drizzle on top.