Prep the pan and oven: Heat oven to 350°F (175°C). Grease and line an 8x8-inch or 9x9-inch square pan with parchment, leaving overhang for easy lifting.

Make the crumb topping: In a bowl, mix 1 cup flour, 1/2 cup light brown sugar, 1/4 cup granulated sugar, 1 teaspoon cinnamon, and a pinch of salt. Stir in 1/2 cup melted unsalted butter until large clumps form. Refrigerate while you make the batter.

Whisk the dry ingredients: In a large bowl, whisk 1 1/2 cups all-purpose flour, 1 teaspoon baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon kosher salt, 2 teaspoons cinnamon, 1/2 teaspoon nutmeg, 1/2 teaspoon ginger, and a pinch of cloves if using.

Mix the wet ingredients: In a separate bowl or large measuring cup, whisk 1 cup pumpkin puree, 2/3 cup granulated sugar, 1/3 cup light brown sugar, 2 large eggs, 1/3 cup neutral oil, 2 tablespoons melted unsalted butter, 1/2 cup milk or buttermilk, and 2 teaspoons vanilla.

Combine: Pour the wet mixture into the dry. Stir gently with a spatula until just combined. Do not overmix; a few small lumps are fine.

Pan and crumb: Spread batter evenly in the prepared pan. Break the chilled crumb topping into big, generous clumps and sprinkle over the batter, covering the surface.

Bake: Bake 33–40 minutes, until a toothpick in the center comes out clean or with a few moist crumbs. The crumb should be golden and crisp.

Cool and glaze (optional): Let the cake cool in the pan for 20 minutes. Whisk 3/4 cup powdered sugar with 1–2 tablespoons milk and 1/2 teaspoon vanilla until smooth. Drizzle over the slightly warm cake.

Serve: Slice into squares. Enjoy warm or at room temperature. The flavor deepens after a few hours.