Preheat the oven to 400°F (200°C) and place muffin liners in a muffin tin or on a baking sheet.
Melt the butter and then immediately pour it into a large mixing bowl together with the sugar. Add vanilla as well, if using a liquid product like extract. Mix until well combined, then mix in the eggs.
1 cup salted butter, 1 cup sugar, 2 eggs
In a separate bowl, mix together the dry ingredients for the batter: flour, vanilla (if using powder/sugar) and baking powder. Then add it to the egg, butter & sugar mixture and mix, but don't mix more than necessary to combine.
2 cups flour, 1 tsp vanilla, 2 tsp baking powder
Add in the milk and mix again, just until the batter has an even and smooth texture.
1 cup milk
Mix together the sugar and cinnamon for the topping. Place the apple slices in a bowl and mix with half of the cinnamon-sugar mixture.
4 Tbsp sugar, 2 tsp cinnamon, 3 small apples
Pour or scoop the batter into the muffin liners. Don't fill them more than to ¾. Then add the apple slices mixed with cinnamon sugar on top, and make sure to press them down a bit into the batter. Sprinkle the remaining cinnamon sugar on top.
Place the muffin tin in the middle of the oven and bake for 18-20 minutes. Test with a cake tester or tooth pick - it should come out with no or very little cake batter when they are done. Remove from the oven, and let them sit for at least 10 minutes before moving from the muffin tin.
Video
Notes
Note on Apples
You can use any kind of apple you like for this recipe. I prefer either Royal Gala, Pink Lady or Honeycrisp - or try a crisper, more tart, green version like Granny Smith.I only add apples on top, but you can also add some diced in the batter. I recommend tossing them in cinnamon sugar first for extra flavor.
Note on Vanilla
You can make this with vanilla powder, vanilla extract or vanilla sugar. All three work in the same amount. If using a liquid product like vanilla extract, add it with the butter instead of with the dry ingredients.Don't overmix after adding the dry ingredients. You can mix all you want before this, but afterwards you want to mix as little as possible. Make sure everything is combined, but not more!Don't bake them too long. Overbaking is the most common reason why muffins come out dry.Bake time can vary with your oven. Test your muffins while baking, especially the first time. I recommend testing the first time after 16 minutes and then every 1-2 minutes. Use a cake tester or a tooth pick - it should come out with no or very little batter, or even a few crumbs, when they're done.Let them cool down before moving. They need to sit for 10 minutes or so before removing them from the muffin tin, to make sure they stay in one piece.
Storing, Freezing & Making Ahead
Make ahead: These muffins are best on the 2nd and 3rd day - so go ahead and make them ahead of time.Storing: Store at room temperature in a muffin tin or plastic bags for up to 5 days.Freezing: Store in the freezer in an airtight container for up to 3 months.Reheating: You can reheat frozen muffins in the microwave, oven or air fryer. Reheat in air fryer or oven at low temperature (around 300°F / 150°C) until just warm and gooey. In the microwave, choose a lower power setting to avoid drying them out.