Combine the butter, flour, sugar, and cinnamon in a bowl. Using either a fork or a pastry blender, cut the butter into the dry ingredients until you have a fine crumb mixture. Set aside.
Preheat oven to 425 F/ 218 C.
Peel and slice your apples. Place half of the apples in the unbaked pie shell, and sprinkle with 2 tablespoons of lemon juice (or more or less, depending on your taste preference and how sweet or tart your apples are). Cover with half of the crumb mixture. Gently shake the crumb mixture down into the crevices between the apples, turning the pie a couple of times and shaking again to get it well distributed.
Place the rest of the apples on top, pour another 2 tablespoons of lemon juice over them, and cover with the remaining crumb mixture.
Bake at 425 F/ 218 C for 10 minutes. Then reduce heat to 350 F/ 177 C and bake for another 45-50 minutes, until thick and bubbly around the edges.
Let cool completely before slicing. Store, loosely covered with foil or plastic wrap, at room temperature for up to 3 days or in the refrigerator for up to 6 days.