Turn the Crockpot on High, and Pour in the lemon filling, 1 cup of the sugar, lemon extract, Vanilla, and Sweetened Condensed Milk, and stir well to blend. Place the lid on the crockpot. In a separate bowl, place the flour, and the other cup of sugar, and stir well to blend. Melt the butter, and stir it into the flour and sugar, to form a crust. Spoon the crust dough over the Lemon Filling in the Crock-Pot, and smooth gently with a spoon. Place the lid on, and leave it for about an hour on high, or until it bubbles, then turns on low and leave for 4 more hours.