Preheat the oven to 350°F (177°C) for convection or 325°F (163°C) for a conventional oven. Line 16 muffin wells with cupcake liners. In a medium bowl, combine flour, cocoa powder, sugar, baking powder, baking soda, and salt. In a separate large bowl, whisk together oil, eggs, and hot coffee until smooth. Sift the dry ingredients into the wet mixture and whisk until a cohesive batter forms. Divide the batter evenly among the liners, filling each about 2/3 full. For the filling, insert a Reese’s cup into the center of each cupcake or add a 5g dollop of peanut butter, pressing it lightly to ensure it’s covered. Bake for 16–18 minutes, until the tops spring back to the touch. Let cupcakes rest in the pan for 10 minutes before transferring to a wire rack to cool completely.

To prepare the buttercream, combine sugar and water in a saucepan over medium heat and allow it to simmer gently with the lid on. Meanwhile, beat the eggs in a stand mixer on high speed until frothy. Once the sugar syrup reaches 240°F (116°C), gradually pour it into the eggs with the mixer on medium speed, avoiding direct contact with the whisk. Increase to high speed and whip until the mixture is pale, fluffy, and cool to the touch, about 5–10 minutes. Reduce speed and add butter a few tablespoons at a time, mixing until smooth. If the mixture appears curdled or doesn’t emulsify, incorporate an additional 1/4 cup butter. Scrape the bowl, then add vanilla, salt, and peanut butter. Whip on high for 1–2 minutes more until the texture is uniform and airy. Transfer to a piping bag fitted with a large round tip and pipe tall swirls atop each cupcake. Freeze for 15 minutes until firm.

For the chocolate shell, combine chocolate chips and oil in a tall measuring cup. Microwave in 30-second bursts, stirring between each, until fully melted. Dip the chilled frosted cupcakes into the chocolate coating and garnish with flakey sea salt, if desired. Allow them to set at room temperature for a softer cupcake and buttercream texture before serving.