Preheat oven to 375 F. Grease a standard 12-cup muffin tin. (Note that this recipe makes about 15 muffins, so you can either use another muffin tin for the remaining muffins, or make 2 batches).
In a large bowl, whisk together the eggs, sour cream, milk, melted butter, and vanilla extract. Set aside.
In a medium bowl, whisk together the flour, sugar, baking powder, and salt.
Stir the flour mixture into the egg mixture with a wooden spoon or rubber spatula.
Put about 2 tablespoons of batter in each cup.
Sprinkle about 1 tablespoon of filling into the cups, on top of the batter.
Add another 2 tablespoons of batter to each muffin cup, over the filling.
Sprinkle another tablespoon of filling on top.
Bake in the preheated oven for 22-26 minutes, until the top springs back when touched and a toothpick inserted in the center comes out clean.
Allow the muffins to cool in the pan on a wire rack for 15 minutes and then transfer to the rack to cool completely.