Preheat the oven to 425°F.

Line a 12-cavity muffin pan with muffin/cupcake liners.

In large mixing bowl, use a hand mixer to cream together the butter, brown sugar, and vanilla extract on medium-high speed until smooth and combined, 1-2 minutes.

Add the eggs and beat for a minute longer, until the mixture is pale and fluffy. Add the sour cream and milk. Continue to beat until fully incorporated, scraping down the sides of the bowl with a rubber spatula.

Add the flour, spices, baking powder, baking soda, and salt to the bowl. Beat the mixture on medium-low speed, scraping down the sides of the bowl with a rubber spatula as needed, until just combined. Do not over-mix.

Peel and core the apples, and finely chop them into 1/4-inch pieces.

Add the apples to the mixing bowl. Use a rubber spatula to fold the apples into the batter until they are well distributed.

Spoon an even amount of batter into each muffin liner.

Bake the muffins on middle rack of oven for 5 minutes.

Reduce the oven temperature to 350°F. Continue baking until a toothpick inserted in the center of a muffin comes out clean, 14-16 minutes.

Check to see that muffins are done. Remove from oven or add time as needed.

Allow the muffins to cool in the pan for 5 minutes before removing and serving. Store leftovers in an airtight container at room temperature for 2 days, or refrigerate for 3 days.