Preheat oven to 375°F /190C. Spray inside of muffin tin with non stick spray or line with paper liners (spraying is better). Peel and dice the apple into small bite size pieces.
In a large bowl, combine all the dry ingredients. Swirl around a whisk to distribute and break up any clumps. Make a well in the center of the flour mixture. Add the eggs, milk, and vanilla. Whisk together, incorporating the flour slowly until smooth. Stir in the melted butter.
Place the prepared muffin pan in the oven to heat up for 5 minutes so that it is hot when you place the batter in.
Just before the pan is ready, add the chopped apples and the vinegar to the batter and stir to evenly distribute. Do not do this step until the last minute – you want the baking soda and vinegar to react in the oven not while sitting out.
Scoop batter into the hot muffin tins (a 1/2 cup measuring scoop is good for this), filling to about 3/4 of the way full.
Place in the oven immediately. Bake for 18 minutes or until a cake tester inserted comes out clean. Do not open the oven for the first 15 minutes of the bake. Allow to sit in the pan for 5 minutes before removing and putting each on a cooling rack.
Make a glaze. Simple is combining 1 cup powdered sugar with just enough milk, water or apple cider vinegar to thin out to the thickness of your liking.
Pour the glaze over the un molded fritters while still hot. Allow to cool for at least 20 minutes before eating.