For the Crust:
2 cups rolled oats
1 cup all-purpose flour
2 teaspoons cinnamon
1/2 cup pecans (chopped)
1/4 cup dark brown sugar
1 teaspoon vanilla
1 cup butter (melted)

For the Filling:
1 cup apple butter
1/2 cup dark brown sugar
1 medium egg
1 teaspoon all-purpose flour
1 1/2 cups sweetened condensed milk

For the Crust: Mix oats, flour, cinnamon, pecans, sugar, and vanilla together in a large bowl.
Pour melted butter over mixture and stir until completely combined.
Press mixture into bottom and sides of pie plate (it will be a thick crust) and refrigerate until ready to use.

For the Filling: Adjust oven rack to center position and preheat oven to 350°F.
Whisk all ingredients in a bowl until well combined. Pour into prepared pie crust.
Bake until crust is golden and a toothpick inserted in the center comes out clean, about 40 minutes.