Small-Batch Lemon Sugar Cookie Bars

Preheat oven to 350° Farenheit and line a 1 pound loaf pan with parchment paper.
In a medium size bowl, cream butter and sugar gether with an electric mixer on medium speed for 2 minutes until light and fluffy.
Add the egg, vanilla extract and lemon zest and mix until fully incorporated, but do not whip the the batter.
Add the flour, baking powder, and sea salt to the bowl and mix until just combined. There sould be no flour remaining.
Carefully press the dough into the bottom of the loaf pan and spread evenly.
Bake cookie bars for 20-22 minutes, until the center is slightly puffed up and the edges are just starting to brown.
Let the cookie bars cool completely in the pan.
While the cookie bars are cooling, cream the butter, powdered sugar, heavy cream, vanilla extract, lemon juice, and lemon zest together in a small bowl until fluffy. If the frosting is too stiff, add a tiny bit of lemon juice or cream to loosen it up. If it's too runny, add a tablespoon or two of powdered sugar to stiffen it up.
Remove cookie bars from the pan and frost. Top with sprinkles or remaining lemon zest and slice into 8 equal size bars.
Store cookie bars in an airtight container for 2-3 days or freeze for up to 3 months.