Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius). Line muffin pans with paper liners and set aside.

In a medium bowl, whisk together peanut butter, oil, sugar, eggs, baking powder, baking soda, and vanilla until combined.

Add milk and cocoa powder. Whisk until fully combined.

Switch to a sturdy spoon and stir in flour. Mix until completely smooth.

Spoon batter into prepared muffin pans, filling each cup about two-thirds full. Set aside.

Mix all ingredients together in a small bowl until the mixture has the texture of a very loose dough.

Divide the crumbs over the muffins, breaking into small pieces as you top them.

Bake for about 20 minutes, until the tops are firm.