Preheat your oven to 350 degrees F and lightly coat the inside of twelve 8-ounce glass jars with non-stick cooking spray.

Whisk together the flour, baking powder, salt, cocoa powder, and sugar in a large mixing bowl until the mixture is uniform in color.

In a separate bowl, combine the melted butter and vanilla extract, then beat in the eggs until the mixture is smooth.

Pour the wet ingredients into the dry ingredients and stir with a sturdy spoon until the batter is just combined and no streaks of flour remain.

Divide the batter evenly among the prepared jars, filling each one about one-third of the way full.

Arrange the jars on a baking sheet so they are not touching and bake for 20 minutes, or until a toothpick inserted into the center comes out clean.

Remove the jars from the oven and let them cool on the baking sheet for 10 minutes before serving.