Preheat the oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners and, if desired, lightly spray the liners with nonstick spray.

In a large bowl combine 1/2 cup VERY hot coffee or hot water with the 1 stick unsalted butter (cut into small cubes and at room temperature) and 1/2 cup semi-sweet chocolate chips. Whisk vigorously until the butter and chocolate are completely melted and the mixture is smooth (let sit 30–60 seconds if needed, then whisk again).

Whisk in the 2 large eggs plus 1 large egg yolk, one at a time, until each is fully incorporated. Then whisk in 1 cup granulated sugar and 1 teaspoon vanilla until combined.

Place a fine-mesh strainer over the bowl with the wet ingredients. Into the strainer add 3/4 cup + 2 tablespoons all-purpose flour (not packed), 1/2 teaspoon baking soda, 1 teaspoon baking powder, 1/2 cup unsweetened cocoa powder, and 1/2 teaspoon salt. Stir the dry ingredients together in the strainer and let them fall into the wet ingredients (sifting into the bowl).

Using a rubber spatula, gently fold and stir the batter until the dry ingredients are just combined. Do not overmix.

Add 1/2 cup full-fat sour cream and 2 tablespoons coconut or canola oil to the batter. Fold until just combined and the batter is uniform.

Divide the batter evenly among the 12 prepared liners, filling each about 3/4 full.

Bake for 16–18 minutes, or until a toothpick inserted in the center of a cupcake comes out clean or with a few moist crumbs. Remove the pan from the oven.

Let the cupcakes cool in the pan for about 5 minutes, then transfer them to a wire rack to cool completely before frosting.

For the frosting: sift together 3 cups confectioners' sugar and 3/4 cup unsweetened cocoa powder into a bowl to remove lumps.

Using a handheld mixer or a stand mixer fitted with the paddle attachment, beat 1 stick unsalted butter on medium-high speed until creamy, about 2 minutes.

Reduce the mixer speed to low. Slowly add the sifted sugar/cocoa mixture in portions, alternating with 2 tablespoons sour cream and 3 tablespoons half and half, until all of the sifted mixture and dairy have been incorporated. Add 1/4 teaspoon salt and 1/2 teaspoon vanilla.

Once everything is added, increase the mixer speed to high and beat the frosting until light, smooth, and creamy, at least 1 minute.

Frost the cooled cupcakes with the prepared frosting and add any desired decorations.

Store cupcakes at room temperature in an airtight container for up to 4 days.