If you don't have buttermilk on hand you can make sour milk. Add 2 teaspoons of lemon juice or plain white vinegar to your measuring cup, then pour the milk in to reach 2/3 cup. Let it sit briefly. This will make sour milk.
If you want to make this in a 9x13 pan you can add an additional 1/2 cup flour and 1/3 cup milk to the recipe. Double the crumb recipe and bake for 40 minutes.
All nutritional information is based on third party calculations and is only an estimate. Each recipe and nutritional value will vary depending on the brands you use, measuring methods and portion sizes per household.
Banana Bread Crumb Cake https://therecipecritic.com/banana-bread-crumb-cake/