adapted (barely)from King Arthur Whole Grain Baking
3/4 cup barley flour
1/4 cup all-purpose flour
1 tablespoon maple sugar
1/4 teaspoon salt
1/2 cup (1 stick) cold unsalted butter, cut into small cubes
1 large egg, lightly beaten
1-2 teaspoons half and half
1/2 cup old-fashioned rolled oats
1 cup water
4 large eggs
1/2 cup maple sugar
3/4 teaspoon salt
1 tablespoon cider vinegar
1 cup maple syrup
4 tablespoons unsalted butter, melted
1/2 teaspoon maple extract
1 cup chopped walnuts
Whisk together flours, sugar, and salt in a medium bowl. Add butter, using a pastry blender or your hands work butter into flour until the mixture resembles coarse crumbs. Stir in the egg. Add one teaspoon of half and half and work into the mixture. Test to see if the dough holds together by squeezing the mixture together. If it still seems dry and crumbly, add the second teaspoon and work it into the mixture. Shape the dough into a disk and pat until it is about 1 inch thick, wrap in plastic wrap and refrigerate overnight or up to 3 days.
Remove the crust from the refrigerator about 30 minutes before you are ready to make the pie. You want the dough to become flexible enough to roll out. Flour your work surface and roll the dough to a 12 inch circle. Place dough in a regular (not deep dish) pie pan. Crimp the edges. Place the crust back in the refrigerator to chill while you are making the filling. Adjust oven rack to the lowest position.Preheat oven to 400 degrees F.
Place oats and water in a small saucepan over medium heat, cook until thick and creamy as they would be for breakfast cereal. Place the oats in a bowl of a stand mixer and set on lowest speed. This will accelerate the cooling of the oats. Make sure the outside of the bowl is only the slightest bit warm before adding the eggs. You don't want the eggs to scramble. Add the eggs, sugar, salt, vinegar, maple syrup, melted butter, and maple extract to the oats. Continue to stir on low speed until all the ingredients are combined.
To make the pie
Pour filling into pie crust and sprinkle the walnuts on top. You will want to place a cookie sheet under your pie as it most certainly will cook over the edge of the pie plate and make a huge smoldering mess of your oven. (I didn't do this) Bake pie on the bottom rack of the oven for 15 minutes at 400 degrees F. Lower oven temperature to 350 degrees F and bake until the center is set, 25 to 35 minutes more. Check pie regularly to make sure the crust is not burning. Cover the crust with foil if it appears to be getting dark. Remove pie from oven and allow to cool for 30 minutes before serving. Serve for dessert or breakfast. Either way, enjoy!