Preheat oven to 350°F (175°C). Grease and line an 8x8-inch baking pan.
In a bowl, whisk together flour, baking powder, baking soda, spices, and salt.
In another bowl, cream butter and sugar until light and fluffy. Beat in eggs one at a time, then mix in pumpkin purée and vanilla.
Gradually fold in the dry ingredients until just combined. Pour batter into the prepared pan.
For the crumble topping, mix flour, brown sugar, and cinnamon. Cut in cold butter until mixture resembles coarse crumbs. Sprinkle evenly over the batter.
Bake for 35–40 minutes, or until a toothpick inserted in the center comes out clean.
Prepare glaze by whisking powdered sugar, milk, and vanilla until smooth. Drizzle over cooled cake before serving.
Notes
This cozy dessert pairs beautifully with coffee or tea. For extra indulgence, serve with a dollop of whipped cream or a scoop of vanilla ice cream.