Preheat oven to 350°F (177°C). Grease the bottom and sides of a 4×8-inch rectangular loaf pan with coconut oil.

In a large bowl combine the egg whites and cream of tartar. Whip until stiff peaks form.

In a separate bowl, cream together maple syrup and coconut oil. Mix in the egg yolks.

Add coconut flour, vanilla, apple cider vinegar, baking soda and salt to the mixture.

Mix until combined.

Mix the batter into the egg whites starting with a little bit at a time. Combine until the batter is completely mixed.

Scoop the batter into the loaf pan and spread the batter evenly in the pan.

In a small bowl mix together all the ingredients for the topping. Spread the mixture over the batter. Swirl parts of the topping into the batter.

Bake for 30 minutes.

The cake is done when a toothpick is inserted and comes out clean. Let the cake cool before slicing and serving.