Preheat the oven to 350°F (175°C). Grease two 8×4-inch loaf pans and line with parchment for easy removal.

In a small bowl, mash the ripe bananas with brown sugar, vanilla extract, and ground cinnamon. Set aside.

In a large bowl, cream the softened butter with granulated sugar until light and fluffy, about 2 to 3 minutes.

Add the eggs one at a time, beating briefly after each addition until incorporated.

Sift together the all-purpose flour, baking soda, and salt. Fold the dry mixture into the wet ingredients gently until just combined, avoiding overmixing.

Stir in the sour cream or Greek yogurt until the batter is smooth.

Fold in the mashed banana mixture until combined. The batter should be thick but spoonable.

Spoon the batter evenly into the prepared loaf pans, smoothing the tops.

Make the crumb topping by combining the flour, brown sugar, and cinnamon in a bowl. Cut in the cold butter until the mixture resembles coarse crumbs.

Scatter the crumb topping over the batter and press lightly to adhere.

Bake for 40 to 50 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Let the loaves cool in the pans for 10 minutes, then remove and cool completely on a wire rack before slicing.