Preheat oven to 350. Line an 8x8 pan with parchment paper.
In a medium bowl, combine all the crust ingredients and work together with a fork until it has small crumbles. Dump into prepared pan. Press down with your hands working the crust all the way to the edge. Bake in preheated oven for 13-15 minutes.
While the crust is baking, prepare the lemon filling.
Combine all filling ingredients in the bowl of an electric mixer. Beat on medium-high speed for 3 minutes. Scrape down the bowl. Pour directly onto hot crust as soon as it's out of the oven.
Return the pan to the oven and bake an additional 20-25 minutes until top does not indent when gently touched.
Remove from oven. Immediately sprinkle with powdered sugar. Cool in pan 1-2 hours. Cut and serve.