Preheat the oven to 350°F. Prepare a 12-cup muffin pan by lining it with parchment paper liners.

Let the butter, cream cheese, eggs, and sour cream come to room temperature.

Mix the almond flour, coconut flour, psyllium husk powder, baking powder, and salt in a small bowl. Set aside.

Use a hand mixer or stand mixer to cream together the butter, cream cheese, and erythritol until smooth. The butter should lighten in color and the erythritol should be completely dissolved.

Continue using the mixer to whip in the eggs, one at a time. Scrape the sides of the bowl as needed.

Stir in the sour cream by hand. Add the dry ingredients and mix to form a thick batter.

Measure in the vanilla extract, lemon juice, peanut butter and apples. Stir to combine.

Divide the thick batter evenly among the wells. Bake for 30 minutes or until just lightly browned and the tops are barely firm to a light touch.

Let cool for at least 30 minutes before serving.