Set your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.

In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.

In a large bowl, whisk melted butter and sugar until smooth. Add eggs and vanilla, and mix until combined.

Pour in milk and hot water. Slowly add the dry mix, stirring until smooth and slightly thin.

In a small bowl, mix peanut butter and powdered sugar until thick and creamy, soft but scoopable.

Fill each liner halfway with chocolate batter. Add a teaspoon of peanut butter filling in the center, then cover with more batter until ¾ full.

Sprinkle chocolate chips on top. Bake for 18–20 minutes, or until a toothpick inserted near the edge comes out clean.

Let cool in the pan for 10 minutes. Serve warm for a gooey center or enjoy once cooled.