Preheat oven to 375° F / 190° C. Lightly grease a 24-cup mini muffin pan* with cooking spray, or line with paper liners. Set aside until ready to use.

In a large bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.

In a separate bowl, use a whisk or electric hand mixer to combine eggs, granulated sugar, Greek yogurt, canola oil, and vanilla extract.

With a rubber spatula, fold the flour mixture into the wet ingredients. Slowly add water and combine until smooth. If batter seems too thick to spoon, add additional water 1 tablespoon at a time.

Add chocolate chips and stir to combine.

Spoon muffin batter into prepared pan. Sprinkle each muffin with sea salt.

Bake in preheated oven for 15 minutes, or until a toothpick comes out clean. Remove pan from oven and transfer to a wire rack to cool completely.

Remove cooled muffins from the pan.

Fit a disposable piping bag with a 1/4-inch round metal tip. Fill bag with one cup of peanut butter.

Turn each muffin upside down and inject it with the peanut butter**, taking care not to overfill. Use a butter knife to scrape away any excess peanut butter.

Serve immediately.

Store leftover muffins in an airtight container at room temperature for up to five days.