Preheat oven to 350 degrees. Line a cupcake pan with liners and set aside.
In a large bowl, add in the mashed bananas, melted butter, yogurt, granulated sugar and brown sugar. Mix on medium by a hand mixer.
Add in the egg and vanilla extract. Mix until combined.
Add in the flour, baking soda, baking powder, and cocoa powder. Mix on low until combined.
Stir in the milk chocolate chips.
Scoop the batter into the cupcake liners.
Place into the preheated oven and bake for 20 minutes or until done. Place a toothpick into the center of the cupcakes and if they come out clean or with moist crumbs, they're done!
Let cool and make the frosting!
Frosting
In a large bowl, add in the butter, cocoa powder, and chocolate extract. Beat with a hand mixer until combined.
Add in the powdered sugar and milk and continue to mix until incorporated.
Once incorporated, turn hand mixer on high and beat for 1 minute until light and fluffy.
Place the frosting into a piping bag with a 1M tip. Pipe swirls on the cooled cupcakes.
Just before serving cupcakes, garnish with the freshly sliced bananas. To prevent browning, sprinkle with fruit fresh or lemon juice.
Notes
To store any leftover cupcakes, with chocolate buttercream frosting, you'll want to store in an air tight container in the refrigerator for up to 3 days.