Heat oven to 350 F and line a 12 cup muffin pan with paper liners

whisk flour sugar cocoa baking soda baking powder and salt in a bowl

whisk egg buttermilk hot coffee oil and vanilla in a second bowl

pour wet into dry and whisk just until smooth and thin with no dry pockets

divide batter evenly among liners filling each about two thirds full

bake until a toothpick comes out clean or with a few moist crumbs 16 to 20 minutes

cool 5 minutes in pan then transfer to a rack and cool completely.

Warm milk in a saucepan until steaming

whisk sugar cocoa cornstarch egg yolks and salt in a bowl until smooth

slowly whisk in the hot milk to temper then return to saucepan

cook over medium heat whisking constantly until thick and bubbling 1 to 3 minutes

remove from heat and whisk in butter chopped chocolate and vanilla until smooth

press plastic wrap directly onto the surface and chill until cold and pipeable 2 hours or up to overnight.

Heat cream until just simmering then pour over chopped chocolate and rest 2 minutes

whisk until glossy then whisk in butter and salt and cool until thick but pourable 10 to 20 minutes

core cooled cupcakes with a small knife or cupcake corer

pipe or spoon chilled chocolate cream into each cupcake

spoon or pipe ganache over tops and let set 10 to 15 minutes before serving.