Start by gathering all your ingredients and make sure your butter and eggs are at room temperature. 

Preheat your oven to 350°F (175°C) and grease your Bundt pan with butter or non-stick spray to ensure the cake releases smoothly once baked.

In a medium bowl, whisk the flour, baking powder, baking soda, and salt until fully blended. This step ensures that the dry ingredients are evenly mixed, giving the cake a light, airy texture.

In a large mixing bowl, beat the unsalted butter, granulated sugar, and brown sugar until the mixture becomes pale and fluffy.

Incorporate the eggs one at a time, ensuring thorough mixing after each addition for a smooth batter. Then, stir in the sour cream and mix until smooth. 

Mash your ripe bananas and fold them gently into the batter to get that rich, sweet banana flavor.

Gradually add the dry ingredients into the wet ingredients, mixing on low speed until just combined. Be careful not to overmix.

Transfer the batter into the prepared Bundt pan. Put the pan in the oven and bake for 50-60 minutes, or until a toothpick inserted in the center comes out clean.

Let the cake cool in the pan for 10-15 minutes before turning it onto a wire rack to cool completely. This helps it set and makes it easier to glaze later on.

In a saucepan over medium heat, melt the unsalted butter until it becomes smooth and begins to bubble gently.

Stir in the brown sugar and let it cook for a few minutes, allowing it to fully dissolve into the butter and form a rich, smooth mixture.

Take the saucepan off the heat, then whisk in the vanilla extract, confectioners’ sugar, and milk until smooth and well combined.

If the mixture is too thick, gradually add more milk until you reach the desired consistency.

Let the glaze cool briefly for a thick, glossy drizzle over the cake.