To make the cupcakes, heat oven to 350º. Line muffin tins with cupcake liners.

In the bowl of a stand mixer fitted with the paddle attachment, combine the sugar, flour, cocoa powder, baking soda and baking powder on low speed. Add the eggs, buttermilk, oil and vanilla and mix on medium speed for 2-3 minutes, or until combined. Reduce speed to low and, with the mixer running, gradually add the coffee. Beat until just combined. Stir with a rubber spatula, making sure to scrape the bottom and sides of the bowl. The batter will be thin.

Fill each liner ⅔ full and bake for 18-20 minutes, until a toothpick inserted in the center comes out clean. Allow to cool for 5 minutes in the pan, then transfer to a wire rack to cool completely.

To make the frosting, puree the strawberries in a food processor and set aside. Combine the egg whites, sugar and salt in the bowl of a stand mixer set over a small pot of simmering water. Whisk constantly by hand until the sugar has dissolved. If you need to test it, rub a small amount between your fingertips. The mixture should feel completely smooth and not at all grainy.

Attach the bowl to the mixer and fit it with the whisk attachment. Mix on low speed and gradually increase to medium-high and mix until stiff (but not dry) peaks form. Continue mixing about 10 more minutes, until the mixture is light, fluffy, glossy and completely cool (touch the bottom of the bowl to test).

With the mixer on low speed, add the butter a couple tablespoons at a time. Mix well after each addition. Scrape the sides and bottom of the bowl with a rubber spatula and increase speed to medium. Mix until the buttercream comes together, knowing that it can take several minutes for this to happen. Swap the whisk for the paddle attachment and beat on medium-low speed for about 2 minutes to remove any air bubbles. With the mixer running, gradually add the strawberry puree and mix just until combined.

Frost cupcakes as desired and top with a strawberry just before serving.