Preheat your oven to 180°C / 350°F. Line a 9x11 inch baking pan with parchment paper.
In large bowl or in the bowl of an electric mixer combine 1 cup butter, 1 cup brown sugar, 2 cups rolled oats, ¾ cup spelt flour, ¾ cup all purpose flour, 2 teaspoons baking powder, 1 ½ teaspoons cinnamon, and ½ teaspoon salt. Mix until the mixture is well combine and crumbly.
Remove half of the mixture and set it aside.
Add the egg to the half you still have in the bowl and blend it in well. Use your hands to press that half evenly into the baking pan (wet your hands with cold water to prevent the dough from sticking).
Toss the bottom crust in the oven and bake for about 10 min, until the edges are starting to brown just ever so slightly.
Remove the cooked bottom crust from the oven, and spread with apple butter or other preserve.
Add 1 cup chopped walnuts to the remaining crumble mixture.
Sprinkle the oat crumble topping over the top evenly. Set the pan back into the oven and bake for about 15 minutes, until the crumble topping is beginning to brown.
Remove from the oven and cool well before slicing. Slice into squares, and enjoy.