Preheat your oven to 350°F (175°C). Line your baking sheets with parchment paper to prevent sticking.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon. Set aside.
In a large mixing bowl, cream together the softened butter, granulated sugar, and light brown sugar until light and fluffy.
Add the egg and mashed bananas to the butter-sugar mixture. Beat until well combined.
Mix in the sour cream and vanilla extract until fully incorporated.
Gradually add the dry ingredients to the wet mixture, mixing until just combined. Be careful not to overmix!
Using a cookie scoop, drop rounded tablespoons of batter onto your prepared baking sheets, leaving space between each for spreading.
Bake in the preheated oven for about 12-15 minutes, or until the edges are lightly golden and a toothpick comes out clean. Let cool on the baking sheets for a few minutes before transferring to a cooling rack.
While the whoopie pies are cooling, prepare the filling by beating together the mascarpone and sugar until smooth and creamy.
Once the whoopie pies are completely cooled, spread a generous dollop of the mascarpone filling on the flat side of one pie and top it with another pie, flat side down. Repeat with the remaining pies.
