For the Oat Cookie (used in the crust):
2/3 c. all-purpose flour
1/8 tsp. baking powder
1/8 tsp. baking soda
1/4 tsp. salt
1/2 c. unsalted butter, softened
1/4 c. light brown sugar, packed
2 tbsp. white sugar
1 large egg
1 cup rolled oats
Heat the oven to 375ºF.
In a medium bowl, sift together the flour, baking powder, baking soda and salt. In the bowl of a stand mixer using the paddle attachment, or in a large bowl using an electric mixer, beat the butter, brown sugar and sugar until light and fluffy. Whisk the egg into the butter mixture until fully incorporated. With the mixer running, beat in the flour mixture, a little at a time, until fully combined. Stir in the oats until incorporated.
Spread the mixture onto a 9 x 13-inch baking sheet and bake until golden brown and set, 18-20 minutes. Remove from heat and cool to the touch on a wire rack. Crumble the cooled cookie to use in the crust.
For the Crust:
Crumbled cookie for crust
1/4 cup butter, room temperature
1/8 teaspoon salt
Combine the crumbled cookie, butter and salt in a food processor and pulse until evenly combined and blended (a little of the mixture clumped between your fingers should hold together). Divide the mixture between 2 10-inch pie tins. Press the crust into each shell to form a thin, even layer along the bottom and sides of the tins. Set the prepared crusts aside while you prepare the filling.
For the Crack Pie Filling:
1 1/4 c. white sugar, granulated
3/4 c. light brown sugar, packed
1/4 tsp. salt
1/3 c. milk powder
1 c. unsalted butter, melted
3/4 c. plus 2 tablespoons heavy cream
1 tsp. vanilla extract
8 large egg yolks
In a large bowl, whisk together the sugar, brown sugar, salt and milk powder. Whisk in the melted butter, then whisk in the heavy cream and vanilla.
Gently whisk in the egg yolks, being careful not to add too much air. Divide the filling evenly between the two prepared pie shells.
Bake the pies, one at a time, for 15 minutes, then reduce the heat to 325ºF and bake until the filling is slightly jiggly and golden brown (similar to a pecan pie), about 10 minutes. Remove the pies and cool on a wire rack. Refrigerate the cooled pies until well chilled. The pies are meant to be served cold, and the filling will be gooey.