Gluten-free White Chocolate Cake

This light, fluffy yellow cake is perfumed with vanilla and white chocolate, which gives it a delicate, fine-textured crumb that slices easily.  It contrasts beautifully with a lemon buttercream frosting, for the perfect indulgence. The texture is best on the day it’s baked, so if you don’t have time to make the frosting and the cake on the same day, make the buttercream ahead of time and bake the cake on the day you plan to serve it. A touch of baking soda helps the crust to brown evenly, which can be a problem in gluten-free baking, especially since I cut the sugar in half.

Gums such as xanthan and guar are often used to duplicate the effects of gluten in baked goods that use yeast, but they aren’t necessary for most quick breads and baked goods that use eggs or baking powder for leavening. Certain types of cake are the main exception. Instead of gluten, these cakes depend upon the interaction between starch and the leavening to form their structure and high starch cake flour is required for success.

Most wheat flour is bleached and maturing agents are added to change the baking properties. Chlorine is used in cake flour to weaken the gluten and increase the ability of the starch to absorb water and swell, which forms thicker batters and stiffer doughs. Chlorine also increases the ability of starch to bind with fats, helping them to spread evenly throughout the batter and produce a finer crumb.

It’s easy to duplicate the high starch content of cake flour using gluten-free ingredients, but unless a gum is used, the starch will not form the proper structure because it can’t absorb enough water to hydrate properly, so the cake won’t rise very high. In addition, the fat in a gluten-free cake made without a gum will not be distributed evenly, making the crumb coarser and denser. This is fine for certain types of cake, but not for a high-ratio cake like the one I adapted for this recipe, which contains more butter and sugar than the typical quick bread or cake.

Gums are hydrocolloidal, which means they form a gel when mixed with water. The choices for gluten-free baking are xanthan gum, guar gum, chia seeds, flax seeds and psyllium husks. Each one has different properties, so  experimentation is needed to find the right one. Many people, including me, dislike the mouth feel and texture of baked goods made with xanthan or flax, while guar and xanthan can cause gastrointestinal upsets. Psyllium, the main ingredient in Metamucil, is getting a lot of good press as a substitute for guar and xanthan, so I decided to try it in a cake. The results were amazing, producing a cake with a fine crumb that rose much higher than the dense cakes made with xanthan. Psyllium can be found in the health care section of stores such as Wal Mart and it’s a lot cheaper than xanthan or guar. Most sources say that it can be substituted on a one for one basis, but I had to double it for this cake.

Weigh your ingredients for quick, accurate measurements that will give you reliable results every time you bake, unlike volume measurements which can vary greatly. Buy high quality white chocolate bars, such as Lindt or Ghirardelli, for best results. White chocolate contains milk, so this recipe may not be suitable for those who are lactose-intolerant.

Gluten-free White Chocolate Cake

Serves 12, adapted from “The Cake Bible”

170 grams (6 ounces) white chocolate
7 large egg yolks (ranges from 112 to 120 grams)
260 grams (1 cup + 1 tablespoon or 255 ml) lactose-free or regular milk, divided
6 grams (1 1/2 teaspoons or 7.5 ml) vanilla
198 grams (1 1/3 cups or 320 ml) superfine brown rice flour
66 grams (1/3 cup or 80 ml) potato starch
36 grams (1/4 cup or 60 ml) tapioca starch
150 grams (3/4 cup or 180 ml) sugar
22 grams (1 tablespoon + 1 1/2 teaspoons or 22.5 ml) baking powder
5 grams (3/4 teaspoon or 3.75 ml) salt
3 grams (2 teaspoons or 10 ml) psyllium husks
1 gram (1/4 teaspoon or 1.25 ml) baking soda
128 grams (9 tablespoons or 135 ml) unsalted butter, softened
1 recipe Lemon Buttercream Frosting
1/3 cup (80 ml) seedless raspberry jam, optional

Grease two 8-inch by 2-inch (20 cm x 5 cm) cake pans. Line the bottoms with parchment or wax paper, then grease again and coat with flour.

Preheat the oven to 375º F (190º C). Break the chocolate into small pieces and put them in a small, microwave safe bowl. Place the bowl in the microwave and set it for 50% power, then heat the chocolate for 1 to 1 1/2 minutes. Remove and stir. Continue heating and stirring in 30 second increments. Stop heating the chocolate when small lumps remain. Stir until the chocolate is smooth.

In a medium bowl, combine the yolks, vanilla, and 60 grams (1/4 cup or 60 ml) milk and whisk lightly. In a large bowl, combine the dry ingredients and whisk until combined. Add the butter and the remaining 200 grams of milk (3/4 cup or 180 ml). Mix on low until the dry ingredients are moistened. Increase speed to medium if using a stand mixer, or high if using a hand-held mixer, and beat for 2 minutes. This will activate the psyllium and develop the cake’s structure, so don’t skip this. Scrape down the beaters and sides of the bowl, then add 1/3 of the egg mixture and mix for 20 seconds. Do this 2 more times, then add the melted white chocolate and mix for another 20 seconds, or until the chocolate is completely incorporated.

Divide the batter between the prepared pans and use a spatula to smooth the surface. Bake for 30 to 40 minutes, or until golden brown and a toothpick inserted in the center of each pan comes out clean. Cool on a wire rack for 10 minutes, then run a knife around the sides to loosen the layers. Carefully invert onto the rack, then flip the layers so that the tops are up, to prevent splitting. Let cool completely before frosting. Optional: add a layer of raspberry jam between the layers.