Make the candied bacon: Preheat the oven to 350 degrees F and set a rack on a foil-lined baking sheet. Whisk the brown sugar, granulated sugar and cocoa powder in a medium bowl. Toss the baconin the sugar mixture until coated, then arrange on the rack in a single layer. Bake until dark brown, 15 to 20 minutes. Let cool, then transfer to a plate and pat dry with paper towels. Chop 6 pieces of the bacon; set aside.
Meanwhile, make the cupcakes: Combine the vegetable oil, espresso, brown sugar, cocoa powder and chocolate in a large microwave-safe bowl and microwave until hot, about 2 minutes. Whisk until smooth, then set aside to cool, about 15 minutes.
Whisk the flour, granulated sugar, baking soda and fine salt in a medium bowl. Add the buttermilk, eggs and vanilla to the cooled chocolate mixture and whisk until smooth. Add the flour mixture and continue whisking until combined.
Line a 12-cup muffin pan with paper liners. Divide the batter among the cups, then sprinkle with the chopped bacon. Bake until the cupcakes spring back when lightly pressed, 20 to 25 minutes. Let cool 10 minutes in the pan, then remove to a rack to cool completely.
Meanwhile, make the frosting: Beat the dulce de leche, cream cheese and vanilla in a large bowl with a mixer on medium speed until combined. Transfer to a pastry bag fitted with a large star tip; refrigerate 30 minutes.
Pipe the frosting onto the cupcakes. Top with the remaining candied bacon, breaking it into pieces; sprinkle with sea salt.