This Banana Bread Coffee Cake is incredibly soft, fluffy and moist with a tender crumb that melts in your mouth. It has the perfect amount of banana flavor with a hint of spice and richness from sour cream. There's a buttery cinnamon crumble on top and an espresso glaze that makes it so special.
Make the crumb topping. Combine flour, brown sugar, cinnamon and salt in a medium bowl and mix together until evenly blended. Add the soft butter and blend it in using your finger tips (you can also use a fork, but I find it works better and faster with my hands) until it reachesa crumbly and clumpy consistency. Do not over mix into paste, but do ensure there is no dry or dusty flour left in the bowl. The crumbs should be irregular, ranging in size from a pea to pecan. Cover the bowl and refrigerate it until needed so it doesn't dry out.
Make the banana bread batter. Mash banana so it is quite smooth and measure out 1 cup (237ml). Place it in a bowl and add brown sugar and granulated sugar. Whisk until smooth. Add eggs and whisk until evenly incorporated. Add melted butter, sour cream and vanilla extract and whisk until combined and smooth.
Combine flour, baking powder, baking soda, cinnamon, nutmeg and salt in a medium bowl and whisk to blend evenly.
Add the dry ingredients and start folding them through gently. Before it is all incorporated and a few streaks remain, add chocolate chips and fold them in.
Assemble the cake. Spread the batter evenly into the prepared pan. Sprinkle the crumb topping mixture evenly over top and sprinkle a few extra chocolate chips over the crumble. Bake for 38-42 minutes until a toothpick inserted into the middle comes out clean. Transfer pan to a wire rack, cover with foil and set aside to cool for at least 30 minutes. The foil will help it steam slightly so that the crumbs soften just a touch but will still stay crunchy.
Once cool enough, lift the cake out of the pan using the overhanging parchment and let it continue cooling on the rack while you make the glaze.
Make the espresso glaze. Combine powdered sugar, espresso powder, cinnamon, salt and vanilla in a medium bowl. Gradually whisk in milk one teaspoon at a time until it is a drizzling consistency. I like when it is runny but still opaque. Slice and enjoy!