Preheat oven to 425 degrees (*note that you will be turning the temp down to 350 degrees after 7 minutes of baking). Generously grease or line muffin tins.
In a mixing bowl, cream butter and sugar. Add the eggs and combine well. Follow by adding the yogurt and vanilla and mixing well.
In a small bowl stir together the gluten free flour, almond flour, baking powder, baking soda, cinnamon and salt.
Add the flour mixture to the wet ingredients with your mixer on a low speed. Once the dry ingredients are incorporated, turn the mixer to a high speed to work out any lumps,
Using a spatula or wooden spoon, gently fold the diced apple into the batter.
Spoon the batter into the muffin tins, filling about ⅔ of the way. Mix the remaining sugar and cinnamon together and sprinkle on top of the muffin batter.
Bake at 425 degrees for 7-8 minutes, watching to be sure they have begun to rise well. Then turn the oven down to 350 degrees and continue to bake for another 10-12 minutes. Once they no longer feel soft in the center, they can be removed from the oven. Let cool in the muffin tins for 5-10 minutes before eating. Sprinkle with a little more cinnamon-sugar if you wish.