Banana bread batter:

1. Before starting, pre-heat your oven to 340F (conventional) and line a light colored 8.5"x4.5" or 9x4" loaf pan with parchment paper and butter/oil. The parchment should rise to the edges on both sides to create "flaps" that can be used to lift the banana bread out of the pan once baked
2. Start by browning the butter. Add the unsalted butter to a saucepan. Place on medium low heat, and cook and stir for ~5-8 minutes until the butter has browned. It will melt first, then become bubbly and foamy before you see brown specks on the bottom and smell a lovely caramel-y scent. It will also stop sputtering once brown. Be sure not to overcook, as it can burn quickly after browning
3. Add the brown butter to a bowl. Add the oil and brown sugar, and whisk for 1-2 minutes. If the mixture feels too hot, wait 5 minutes before proceeding. It's ok if it's grainy!
4. Add the eggs, vanilla, and instant coffee dissolved in water. Whisk for 1-2 minutes until the mixture becomes smooth and lighter in color
5. Add the mashed bananas and greek yogurt, and whisk until combined
6. Sift in the flour, baking powder, baking soda and salt. Gently whisk until the dry ingredients are combined and no lumps or streaks of flour remain
7. Lastly, fold in the chocolate chips. Do not over-mix

Brownie batter:

1. For the brownie batter, melt the butter in the microwave in 15 second increments. Add the melted butter and sugar to a bowl. Whisk with a hand whisk for about 60 seconds or until the mixture looks smooth
2. Add the egg and whisk again until the mixture looks smooth
3. Now sift in the flour, cocoa powder, baking powder and salt directly into the bowl
4. Gently mix in the dry ingredients using slow folding motions until just combined. Do not over-mix to prevent gluten formation
5. Lastly, add in chocolate chips and fold until evenly dispersed

Assembly and baking:

1. To assemble, transfer the brownie batter into a piping bag and cut a 1/2" hole at the tip. You can also use a cookie scoop or spoon instead of a piping bag to add the batter in dollops if you like!
2. Add a third of the banana bread batter to the bottom of the prepared loaf pan and spread it out. Then pipe on two thick strips of the brownie batter. Cover with another third of the banana bread batter and 2 more strips of brownie batter, making sure the brownie batter doesn't touch the edges of the pan. Add the last third of the banana bread batter, and pipe the remaining brownie batter in one strip in the middle
3. Use a skewer to swirl the layers of batters together - I don't like to swirl too much because I like having big pockets of brownie batter
4. Optionally, you can cut some butter into very thin strips and arrange them in a line down the middle of the pan. This helps guide the crack of the banana bread as it bakes. You can also sprinkle over some more chocolate chips
5. Bake in the pre-heated oven for ~65-70 minutes, or until a toothpick inserted in the middle of the banana bread comes out with light, moist crumbs (no wet batter)
6. Let the banana bread cool down in the pan for at least 30 minutes before removing, slicing and serving!

Video tutorial:

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