1-1/3 cups all-purpose flour
1/2 tsp. salt
1/8 tsp. baking powder
1/4 cup butter, chilled
1/4 cup shortening, chilled
1/4 cup ice water, approximately
1 tsp. cider vinegar
1 egg white
2 tbsp. butter
1 leek (white and pale parts only), thinly sliced
2 apples, peeled, cored and cut into small chunks
2 large eggs
3/4 cup half-and-half
1/4 tsp. fresh ground black pepper
1/2 cup (3 oz.) Blue cheese, crumbled
1/4 cup chopped walnuts
Measure dry ingredients into food processor bowl. Pulse to mix. Cut butter and shortening into pieces and add. Process just until mixture resembles coarse meal. Pour flour mixture into a large bowl (preferably a chilled bowl). Combine ice water and vinegar and sprinkle on flour mixture gradually, tossing gently until dough holds together. Form into a flat disk and refrigerate at least 30 minutes.
Sprinkle work surface with whole wheat flour (whole wheat flour will not toughen dough and gives extra flavor). Place pastry disk on surface and roll to form a 12-inch circle. Fold into quarters and lay in 9 1/2" tart pan. Unfold and press dough against bottom and sides of pan. Cover with plastic wrap and chill at least one hour. Preheat oven to 400°. Cover dough with non-stick aluminum foil and fill with dried beans or pie weights. Bake until the dough is baked through but not browned, about 20 minutes. Remove foil and beans and continue baking for 8-10 minutes. Remove from oven and cool slightly. Brush with egg white to seal.
Filling and assembly
Melt butter in a skillet, add leek and apple. Cook over medium heat, stirring until apples are soft, about 5 minutes. Remove and cool. Whisk together the eggs, cream and pepper. Place a cookie sheet on the bottom rack of oven, preheat to 325°. Evenly spread the leek/ apple mixture in the baked tart shell, sprinkle with cheese crumbles and pour mixture over the top. Top with chopped walnuts and bake on cookie sheet until filling has just set in the middle, about 30-40 minutes.