Preheat your oven to 350 degrees.
Mix together the peanut butter, sour cream, & brown sugar. Beat in the eggs, milk, & vanilla extract. Gently stir in the flour until just combined, being careful not to over mix. Spoon the batter into 12 donut pan cavities.
Bake for 8-10 minutes. Cool slightly on a wire rack. Once you're able to comfortably handle them, go ahead and glaze them.
Melt the chocolate chips in the microwave, 30 seconds at first; then stir. Microwave in 15 second intervals, stirring each time, until they're melted. Dip one side of the donut into the melted chocolate & sprinkle with chopped Reese's Cups while the glaze is still wet.