01 -
Heat oven to 350°F. Line 8x8-inch baking pan with parchment paper in perpendicular sheets, leaving overhang.
02 -
Melt butter, mix with brown sugar, baking powder, and salt. Stir in oats and flour. Reserve 1 cup for topping.
03 -
Press remaining mixture into pan. Bake until lightly browned, 12 to 14 minutes.
04 -
Mix lemon zest, juice, sweetened condensed milk, and remaining salt until smooth.
05 -
Pour filling over hot crust, top with reserved crumble. Bake 22-24 minutes until edges are browned.
06 -
Cool completely (1.5 hours), optional refrigerate 30 minutes to firm. Cut into 12 pieces.