Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.

In a medium bowl, whisk together flour, baking soda, and salt until well-blended.

In a large bowl, cream softened butter with granulated and brown sugar until light and fluffy, about 3-5 minutes.

Mix in vanilla extract and mashed banana until fully combined.

Gradually fold dry ingredients into wet mixture until just combined. Chill dough for about 15 minutes.

Scoop chilled dough onto prepared baking sheets, spacing them about 2 inches apart.

Bake for 10-12 minutes or until edges are golden. Let cool on a wire rack.

Whip heavy cream until thickened. Gradually add powdered sugar, vanilla, pureed banana, and lemon juice until soft peaks form.

Pipe cream filling onto the flat side of half the cookies and sandwich with another cookie.

Dust with powdered sugar before serving.