Preheat the oven to 350 degrees F (175 degrees C), coat a 9-inch square baking pan with cooking spray, line with parchment paper, and coat again with cooking spray.

Combine flour, baking soda, and salt in a medium bowl.

Mash bananas in a large bowl. Add melted butter and sour cream, then stir in brown sugar, eggs, and vanilla until smooth.

Blend dry ingredients into wet mixture. Fold in caramel bits and transfer batter to prepared pan.

Bake for 45 to 55 minutes, checking for center firmness. Let cool on a wire rack.

Prepare crumb topping by crushing shortbread cookies and mixing them with melted butter and salt.

Create caramel glaze by melting butter, adding brown sugar, and simmering with milk. Remove from heat and whisk in powdered sugar, vanilla, and salt until smooth.

Spread caramel glaze evenly over the cooled cake and immediately sprinkle with crumb topping. Let sit until set.