Enjoy this delicious crumb cake as a midday snack or as an after-dinner dessert.
In a small bowl, combine the confectioners' sugar with the flour and butter and pinch to form crumbs. Stir in the toffee bits.
Preheat the oven to 350°. Spray a 10-inch springform pan with vegetable oil cooking spray. In a medium bowl, whisk the flour, baking powder, baking soda and salt. In a large bowl, using a handheld electric mixer, beat the butter until creamy. Add the granulated sugar and beat at medium speed until light and fluffy. Then beat in the eggs and vanilla. Add the sour cream and bananas; beat at low speed just until blended. Add the dry ingredients and beat until smooth. Scrape the batter into the prepared pan and smooth the top.
Sprinkle the crumbs evenly over the batter and bake for 1 hour and 10 minutes, or until the crumb cake is golden and a toothpick inserted in the center comes out with moist crumbs attached. Loosely cover the cake with foil during the last 20 minutes. Let cool in the pan for 15 minutes, then remove the ring and let cool completely before serving.
The crumb cake can be stored at room temperature in an airtight container for up to 1 week.