Preheat oven to 350°F. Spray a Bundt pan really well with nonstick spray.

In a medium saucepan (you need room for the mixture to foam up), combine the stout and molasses over medium heat. Bring to a boil, then remove from the heat and stir in the baking soda. Set aside until the foam subsides and the mixture cools slightly.

In a large bowl, whisk together the eggs, sugars, oil, pumpkin puree and ginger. In a medium bowl, whisk together the flour, ground ginger, baking powder, cinnamon, allspice, nutmeg and salt.

Add about a third of the dry ingredients to the egg mixture and stir just until combined. Add half the molasses mixture, then another third of the dry ingredients, the rest of the molasses mixture and the rest of the dry ingredients, stirring after each addition just until combined.

Pour the batter into the prepared pan and bake for an hour, until the top is springy to the touch. Cool for a few minutes, then invert onto a wire rack while still warm. Cool completely before spreading with cream cheese frosting.

To make frosting: In a large bowl, beat the butter and cream cheese with an electric mixer until creamy. Gradually add the icing sugar, milk and vanilla, beating until the mixture is creamy and well-blended.

Add a little more sugar or milk if necessary to achieve a spreadable frosting.