Rhubarb Crumble Pie

Bahan-bahan (8 porsi)

• 1 single pie crust
• 6 tablespoons all-purpose flour (divided)
• ⅔ cup granulated sugar (+ 1 tablespoon, divided)
• 5 cups chopped fresh rhubarb
• 1 lemon (zest only, optional)
• ⅓ cup all-purpose flour
• 3 tablespoons brown sugar (packed)
• 3 tablespoons granulated sugar
• ½ teaspoon cinnamon
• ⅓ cup cold butter