Preheat oven to 350°F and grease a 9x13-inch pan.
Mix melted butter and sugar. Add eggs and vanilla and mix until combined. Stir in flour, baking powder, salt, milk, and pumpkin until smooth. Pour into the pan.
Mix the topping ingredients together and spoon over the batter. Swirl with a knife.
Bake for 30–35 minutes, or until a toothpick inserted in the center comes out clean.
Whisk together the glaze ingredients and drizzle over the warm cake. Serve warm or at room temperature.
