Preheat oven to 325°F and grease a mini muffin pan with non-stick spray or fill with mini parchment liners.
In a microwave-safe bowl, heat and stir the chocolate chips and butter in 30 second intervals until smooth.
Whisk the sugar into the warm chocolate mixture until it's cool and homogenous (about 2 minutes). Stir in the eggs.
Gently fold the flour, cocoa powder and salt into the wet ingredients using a spatula just until all flour streaks have disappeared.
Using a small cookie scoop or spoon, fill each well of the prepared pan ~½ full with brownie batter. Then, press a mini peanut butter cup into each one.
Bake for 9-12 minutes, or until the edges look slightly firm and dry.
Let the brownies cool in the pan for about 10 minutes and then remove them. If your pan is greased well and slightly warm, you should be able to give them a little twist and pull them right out. Otherwise, you might need to carefully scoop them out with a knife.
Notes
Regular Muffin Pan: These can also be made in a regular-sized muffin pan. Feel free to use regular peanut butter cups as well. Each one will use more batter so it won't make as many and they may need to bake for longer.Measuring Dry Ingredients: Use a scale to weigh the flour for the most accurate and best results. Otherwise, scoop and level with measuring cups.Storage: Store in an airtight container at room temperature for up to 1 week or in the freezer for up to 1 month.Nutrition: The provided nutrition information is an estimate, the calorie accuracy is not guaranteed.