- For the cake, preheat the oven to 275°F. Grease and flour a 10-cup bundt pan.
- In a mixer fitted with the paddle attachment (or with an electric mixer), blend the brown and granulated sugar with the orange zest (the friction of the sugar will draw out the flavor in the orange). Sift in in the flour, salt, baking powder and baking soda. Add the butter and blend in until pieces of butter are no longer visible.
- In a separate bowl, whisk the eggs, sour cream and vanilla. Add this all at once to the flour mixture and blend first on low speed to incorporate, then on medium speed for two to three minutes more. Scrape the batter into the prepared pan, spread to level it, and bake for 20 minutes at 275°F, then increase the heat to 325°F and continue to bake the cake for another 50-60 minutes, until a tester inserted in the centre of the cake comes out clean. Allow the cake to cool for 20 minutes on a cooling rack, then turn the cake out to cool completely.
- For the icing, melt the butter in a saucepan over medium heat until it sputters and then turns brown, about four minutes. Remove the butter from the heat and strain through a coffee filter or other fine strainer.
- While still warm, whisk the butter into the icing sugar and whisk in the water, orange zest and vanilla until smooth. If the glaze is runny, just let it cool a little. Pour this over the cooled cake, coaxing it to drip over the sides. Sprinkle the cake with sea salt and Skor bits (if using) and let the icing set for about an hour.
The cake will keep, well-wrapped for up to four days, or can be frozen for up to three months (do not refrigerate).