Creamy Lemon Crumb Squares

Mix butter and brown sugar until well combined. Sift together flour, salt, and baking powder. Add oats and flour to butter/sugar mixture and mix to combine. Press half of crumb mixture into the bottom of an 8 x 11 inch pan. Mix together condensed milk, lemon juice, and lemon zest. Spread onto the bottom layer of the crumb mixture. Top with the other half of the crumb mixture, but don't press. Bake for 20 to 25 minutes, or until golden brown. Allow pan to sit on counter for 30 minutes after baking. Cut into squares and refrigerate for a couple of hours or until cool. Serve cool.