Heat the oven to 350°F (175°C). Thoroughly grease and flour a 10- to 12-cup Bundt pan, making sure to cover every ridge and the center tube, or coat it generously with baking-release spray.

Whisk the all-purpose flour, baking soda, and salt together in a medium bowl. Set the dry mixture aside while you prepare the wet ingredients.

Beat the softened butter and granulated sugar for 2 to 3 minutes, until light and fluffy. Add the room-temperature eggs one at a time, beating well after each addition, then mix in the vanilla extract.

Beat in the mashed bananas and sour cream until evenly incorporated. The mixture may look slightly textured because of the bananas, which is completely fine.

Add the dry ingredients in two or three additions, mixing only until no dry streaks remain. Avoid overmixing, since excess stirring can make the finished cake dense.

Pour the batter into the prepared Bundt pan and smooth the top. Bake for 50 to 60 minutes, or until a toothpick inserted near the center comes out clean or with a few moist crumbs.

Let the cake cool in the pan for 10 to 15 minutes. Invert it onto a wire rack and allow it to cool completely before adding the glaze.

For the glaze, melt the butter in a saucepan over medium heat. Stir in the brown sugar and milk or cream, bring the mixture to a gentle boil, and cook for 1 to 2 minutes while stirring constantly.

Remove the glaze from the heat and stir in the vanilla. Let it cool briefly until slightly thickened, then drizzle it over the cooled cake and allow it to set before slicing.