No matter how you choose to make this cake, gluten-free or not, it is delicious. It's buttery and even though it looks dense it retains a lightness. The egg and milk wash topping give the final cake a custard note that is really nice. I give you weights for the ingredients. Here is why. In the original recipe it calls for 4 cups of all-purpose flour at 475 grams. Not all flours weigh alike. Weighing out 4 cups of King Arthur Gluten Free Flour, it weighed in at 600 grams. When baking I like to use a scale. While it is backwards and I should have used less gluten free flour I didn't. I went with 600 grams of gluten free flour just to see what would happen and, again, I really liked the result. You can use either flour, it is your choice. You will also notice it calls for salted butter. That is not the norm in baking. It is not a mistake. Without the salt this cake won't be the same so purchase salted butter. —thirschfeld
grams King Arthur all-purpose gluten-free flour (4 cups) or 4 cups all-purpose flour
Sift the flour and cornstarch into the bowl of a mixer. Add the sugar and butter. Use a rubber spatula and scrape every bit of butter off the butter wrappers and put it into the bowl too. Then, using the paddle attachment, mix until combined. Add the yolks and rum. Mix till smooth.
Using one of the butter wrappers grease the inside of a 9 inch ring mold that is 2 inches deep or spring form pan. If you use a spring form pan, dust it with flour after greasing and tilt and shift the pan so you get the sides dusted too. Shake out the excess.
Using a spatula, scoop the batter into the mold then spread the batter out evenly. You may need to moisten the spatula with a little water to keep the dough from sticking to it.
Using the tines of a fork make a cross hatch pattern on the surface of the cake. Using a pastry brush gently paint the top of the cake with the yolk and milk wash.
Bake the cake for 45 minutes. Keep an eye on it and if it starts to brown to quickly reduce the heat. The top should brown and it should be firm to the touch. Remove the cake from the oven and let it cool completely before removing the ring.