Preheat the oven to 350℉ (177℃). Line a 9x9-inch square pan with parchment paper or spray with baking spray.
To make the crumb topping, whisk together the flour, brown sugar, granulated sugar, and cinnamon in a medium bowl. Add the butter, stirring until evenly moistened and the mixture clumps together in moist clusters or crumbs. Set aside in the fridge to chill while preparing the cake batter.
1 1/4 cups (176g) all-purpose flour, ¾ cup (150g) light brown sugar, ¼ cup (50g) granulated sugar, 1½ teaspoons ground cinnamon, ½ cup (113g) salted butter, melted
To make the pumpkin batter, whisk together the flour, granulated sugar, brown sugar, baking soda, baking powder, salt, cinnamon, nutmeg, ginger, and cloves in a large mixing bowl.
1¾ cups (247g) all-purpose flour, ¾ cup (150g) granulated sugar, ¼ cup (100g) packed brown sugar, 1 teaspoon baking soda, ½ teaspoon baking powder, ½ teaspoon salt, 1 teaspoon ground cinnamon, ½ teaspoon ground nutmeg, ¼ teaspoon ground ginger, ⅛ teaspoon ground cloves
In a separate bowl, whisk together the butter, oil, pumpkin, eggs, milk, and vanilla.
¼ cup salted butter, melted, ¼ cup vegetable oil, 1 cup (244g) pumpkin puree, 2 large eggs, ¼ cup milk, 2 teaspoons pure vanilla extract
Add the wet ingredients to the dry ingredients, mixing by hand until just combined and no streaks of flour remain. Pour the batter into the prepared pan. Sprinkle the crumb mixture evenly over the top of the cake.
Bake for 30-35 minutes or until a tester inserted into the cake comes out with just a few crumbs clinging to it. Do not overbake. Let cool.
Once the cake has cooled, whisk together the powdered sugar, cream, and vanilla in a small bowl. Drizzle over the top of the cake and serve warm or at room temperature.
1 cup (120g) powdered sugar, 2 Tablespoons heavy cream or milk, ¼ teaspoon pure vanilla extract