Maple Walnut Bundt Cake

Preheat the oven to 350°F. Butter and flour a 10-cup bundt pan, making sure to tap out excess flour.
Whisk together the flour, baking powder, baking soda, and salt until well blended.
Place the softened butter and brown sugar in the bowl of a stand mixer fitted with the paddle attachment. Cream the butter and sugar on medium-high speed for 10 minutes. The mixture should be pale, thick, very fluffy, and almost doubled in volume.
Scrape down the sides of the bowl, then add the eggs one at a time. Put a couple tablespoons of the flour mixture with each egg to prevent the batter from curdling.
Mix in the maple syrup, molasses, and vanilla extract.
Alternately add the flour mixture and sour cream to the batter, scraping down the sides as needed. Gently fold in the walnuts with a flexible spatula.
Carefully pour the batter into the prepared bundt pan and level the surface.
Bake at 350°F for about 45 minutes, until it is well risen and nicely browned. A toothpick inserted in the deepest part should come out clean.
Let the cake cool for 10 minutes in the pan, then turn it out onto a wire rack to cool completely, about 1 hour.

Sift the icing sugar into a bowl to remove any lumps, then gradually stir in the maple syrup until a thick icing has formed.
Spoon the icing over the cooled cake, allowing it to drip down the sides a little.
Let the icing set for 10-15 minutes, then slice and serve with a cup of tea or coffee.