This can be done with a stand mixer or by hand with a hand mixer or whisk but it is more of a 2 bowl method than one if going the hand mixing route

Preheat oven to 350F with rack in the center.

Place paper baking cups in regular sized muffin tins, spray edges around cups lightly with cooking spray. If you have a small 6 cup muffin tin and you only get 27 or 28 cupcakes fill the rest of the wells halfway with water and no baking cup

Whisk together the dry ingredients (sugar, flour, cocoa powder, baking soda and salt) in a large bowl.

In a large bowl or bowl of stand mixer whisk eggs till slightly thickened and a pale color. 2-3 min

Add in the milk, vanilla, oil and vinegar and whisk/beat well

Add in the melted and cooled chocolate and whisk/beat until combined well

Either add the flour mixture into the wet ingredients OR the wet into the flour and mix just to combine. Add in the boiling water and mix again just to combine. Scrape down the sides of the bowl with a spatula to make sure all the dry ingredients are incorporated

Divide the batter evenly among the muffin cups

Bake 15-18 minutes or until toothpick inserted in the middle comes out clean and free of crumbs or the cupcake tops bounce back when lightly pressed. Mine baked for 18 minutes.

Let cool for 5 min in pans and then remove carefully to a wire cooling rack. Cool completely before frosting