For the press-in crust:
8 tablespoons unsalted butter (1 stick), melted and cooled slightly
1 tablespoon vegetable oil
1 tablespoon granulated sugar
1/4 teaspoon fine salt
1 1/3 cups all-purpose flour, plus more as needed
For the filling:
1 (15-ounce) can pumpkin purée (not pie mix), or 2 cups homemade pumpkin purée
1 cup heavy cream
1 cup maple syrup
2 large eggs
1 teaspoon ground cinnamon
1/4 teaspoon ground ginger
1/4 teaspoon ground nutmeg
3/4 teaspoon fine salt
For the streusel:
1/3 cup packed dark brown sugar
1/4 cup all-purpose flour
1/4 cup uncooked rolled oats (not instant)
1/4 teaspoon ground cinnamon
1/8 teaspoon ground ginger
1/8 teaspoon ground nutmeg
1/4 teaspoon fine salt
3 tablespoons cold unsalted butter, cut into small pieces
For the press-in crust:
Stir the butter, oil, sugar, and salt together in a medium bowl until evenly combined. Add the measured flour and stir until a soft dough forms.
Sprinkle the dough in small clumps over the bottom of a 9 1/2- to 10-inch deep-dish pie plate. Using a measuring cup or your fingers, evenly press the dough into the bottom and up the sides of the plate (flour the cup or your fingers occasionally to prevent sticking).
Cover with plastic wrap and chill in the refrigerator for at least 30 minutes.
Meanwhile, arrange an oven rack in the lower third of the oven. Place a baking sheet on the rack and heat the oven to 375°F. Make the filling.
For the filling and baking:
Place all of the filling ingredients in a large bowl and whisk until smooth and combined. Set aside until the crust is chilled.
When the crust is ready, pour the filling into it. Place the pie on the hot baking sheet and bake until the outer 2 inches of the pie are set, about 50 minutes. Meanwhile, make the streusel.
For the streusel:
Whisk everything except the butter in a medium bowl until evenly combined. Add the butter and, using your fingers, squeeze the flour mixture and butter together until they form moist clumps and all of the flour is totally incorporated into the butter. (Make sure there are no dusty bits at the bottom of the bowl.) Cover and place in the refrigerator.
After the pie has baked for 50 minutes, remove it from the oven and sprinkle evenly with the streusel topping, breaking up any large clumps with your fingers as you sprinkle.
Return to the oven and bake until the streusel lightly browns and the filling is set, but still jiggles slightly in the ce