Preheat oven to 375℉. Grease a 9x13-inch casserole dish with non-stick spray.
Make crust
Mix together the crushed pretzel, graham crackers, brown sugar, vanilla, and butter. Pour crumb mixture into the prepared baking dish and press flat with the bottom of a flat glass.
Bake the crust for 10 minutes at 375℉. Cool completely.
Make 2nd layer
In the bowl of a stand mixer or hand mixer, beat cream cheese until smooth. Add the powdered sugar and beat until smooth.
Carefully fold in the Cool Whip.
Spread the cream cheese mixture over the completely cooled pretzel crust.
Spread the lemon filling over the cream cheese mixture.
Cover and refrigerate for 4 hours or overnight.
Store leftovers in an airtight container in the refrigerator for 3 days.