- Preheat the oven to 350 ºF (180 ºC) and grease a 12-cup (3 L) bundt or Kugelhopf pan.
- Sift the flour, granulated sugar, 2 ½ tsp of the baking powder, baking soda, cinnamon, ginger and salt into a large mixing bowl.
- In a separate bowl, whisk the pumpkin puree, ¾ cup (175 mL) of the buttermilk, brown sugar, eggs and oil and add this to the dry mixture, whisking until smooth. Divide the batter in half and add the cocoa powder, remaining ¼ cup of buttermilk and ¼ tsp (1 g) of baking powder into one bowl until evenly combined.
- Dollop alternating large spoonfuls of pumpkin and chocolate batter into the pan, until both batters are used up. Use a skewer to swirl the batter a little bit. Bake the cake for 60-75 minutes, until a tester inserted in the centre of the cake comes out clean. Cool the cake for 30 minutes in the pan and then tip it out onto a rack to cool completely.
- For the glaze, melt the butter and cook it until it browns, about 2 minutes. Strain the particles out and place the browned butter in a clean pot and add the brown sugar and 2 Tbsp (30 mL) of the milk and bring to a full boil while stirring. Pour this over the icing sugar in a bowl, add the vanilla and stir until cooled enough to be glaze consistency – if it seems too thick, you can add the remaining 1 Tbsp (15 mL) of milk, a little at a time, until you get the right consistency (it should be somewhat fluid but not runny.) Pour this overtop of the Bundt so that it drips partway downs the sides. Leave the glaze to set for an hour before slicing.