• Preheat oven to 350 degrees. Line a loaf pan with parchment paper. Allow to drape over the sides.

Vanilla Batter

• Sift gluten-free flour, baking powder, and salt in a medium-sized bowl.
• In a separate bowl, mix egg yolks, 1 cup of sugar, unsweetened applesauce, sour cream, vegetable oil, and vanilla extract until well combined.
• In a stand mixing using whisk attachment, whip egg whites on medium-low until foamy. Then increase speed to medium-high and whisk until the egg whites are billowy mounds. Gradually add 1/2 cup of sugar and whisk until stiff peaks form.
• Using a spatula, gently fold the egg yolk mixture into the egg white mixture. Then slowly fold the flour mixture into the batter and mix until combined.

Chocolate Batter

• In a separate bowl, whisk together the dutch style cocoa powder, sugar, instant coffee, and boiling water until smooth.
• In a microwave-safe bowl, melt the unsweetened chocolate.
• Gently fold in about half of the vanilla batter until well combined.
• Alternate spooning the chocolate and vanilla batters into checkerboard pattern in the prepared loaf pan. After all of the batter is in the loaf pan, use a wooden skewer to swirl the two batters together into a marble pattern.
• Bake for about 60-70 minutes until an inserted toothpick comes out clean. Remove from oven and allow to cool in the pan for 10 minutes. Using the parchment paper remove the cake from the loaf pan and place a wire rack to cool completely.
• Slice to desired thickness and serve.