Preheat & Prep: Preheat your oven to 350°F (177°C). Line an 8x8-inch metal baking pan with parchment paper, leaving an overhang on the sides. Lightly spray with nonstick cooking spray.
Make the Crust: In a medium bowl, whisk together melted butter, granulated sugar, vanilla extract, and salt. Stir in the flour until a soft dough forms.
Bake Crust: Press dough evenly into the bottom of the prepared pan. Bake for 18–20 minutes, or until the edges are lightly golden brown.
Whisk Filling: While the crust bakes, whisk sugar and flour together in a large bowl. Add eggs, fresh lemon juice, and lemon zest. Whisk vigorously until smooth.
Bake Lemon Layer: Remove crust from oven and pour filling directly onto the hot crust. Reduce oven temperature to 325°F (163°C). Bake for 18–22 minutes, or until the edges are set and the center has a slight jiggle when the pan is gently moved.
Cool & Chill: Cool completely at room temperature on a wire rack, then cover and chill in the refrigerator for at least 2 hours until firm.
Slice & Dust: Lift out using parchment overhang, dust with powdered sugar, and slice into 16 squares with a sharp knife.
