Preheat oven to 350°

In a medium mixing bowl, whisk together flour, rolled oats, salt and baking soda.

Stir in granulated sugar and brown sugar and mix until no clumps of sugar remain. Stir vanilla into melted butter and pour mixture over dry ingredients.

Sprinkle half of the crumb mixture into the bottom of a greased 8 by 8-inch baking dish and gently press into an even layer.

Bake in preheated oven 15 minutes. Remove from oven and set aside (leaving oven heated at 350 degrees).

In a mixing bowl, whisk together sweetened condensed milk, lemon zest, lemon juice, egg yolks and lemon extract until well blended.

Pour mixture over crumb crust in baking dish and spread into an even layer.

Sprinkle top evenly with remaining crumb mixture.

Remove from oven and allow to cool at room temperature, once cool cover and refrigerate 30 minutes - 1 hour, then remove and cut into squares.

*If using salted butter reduce salt amount to 1/8 tsp