Preheat the oven to 350°F. Coat a 24-cup muffin pan with non-stick spray or line it with baking cups.
In a medium mixing bowl, sift the cake flour and baking soda together and set aside.
In a large mixing bowl, beat the egg whites and cream tartar until very foamy, but not stiff. Continue to beat, gradually adding in the sugar. Add the vanilla and oil, then the egg yolks, one at a time. Lastly, add the flour mixture to the bowl.
Fill muffin cups to 2/3 way full with batter. Bake 12 to 15 minutes, or until a toothpick inserted in the center of a cake comes out clean. Set aside to cool and prepare the honey butter.
Combine the honey, butter and a pinch of salt and stir to mix thoroughly. Serve at room temperature with homemade sponge cake muffins and a steamy, hot cup of cocoa or Kona coffee.