A deep, dark gingerbread bundt cake with a tangy cream cheese frosting, perfect for the holidays or for any time in winter when you need some comfort.
Preheat your oven to 350 degrees F. Very generously butter a 12-cup bundt pan and set aside. Don't skip this - this is a very sticky cake.
In a large saucepan, bring stout and molasses to a boil. Remove from heat, whisk in baking soda (note it will begin bubbling vigorously), then cool for a few minutes (to just above room temperature, so you don't cook the eggs when you mix it in later).
In a medium bowl, whisk together the flour, baking powder, and spices. In a separate large bowl, whisk together the eggs and both sugars. Whisk in canola oil, then cooled molasses mixture. Finally, add the flour mixture and stir together (or fold with a spatula) until just combined.
Pour batter into the prepared bundt pan and tap it on the on counter a few times to eliminate air bubbles. Bake the cake until a toothpick comes out with just a few moist crumbs attached, about 50 minutes.
Cool cake COMPLETELY in pan on a rack. Run a butter knife or spatula along the outer and inner edges of the cake, and turn out onto a plate.
In a large bowl, using an electric hand mixer, cream together the cream cheese and butter until fully combined and fluffy. Beat in sugar and salt until fully combined. Add milk, 1 tablespoon at a time, until the frosting is still thick but pourable (it took about 5 tablespoons for me).
Pour frosting evenly over the cake. Dust with cinnamon, if desired. Store in the fridge for up to 5 days; this cake gets better as it sits. Bring to room temperature before eating.