Pre-heat oven to 350F. Line a 12-cupcake pan with cupcake liners or grease it with butter and flour.
Sift flour, cocoa powder, sugar, baking soda, baking powder, and salt together in a large bowl.
In another bowl, mix coffee, vinegar, vanilla and oil. Pour wet mixture over dry. Whisk briefly, until incorporated. Be careful not to overmix. As soon as you see no more streaks of dry mixture, stop whisking.
Distribute batter evenly in cupcake pan. Bake for 15-20 minutes.
Remove and let it cool.
Cashew Pastry Cream
Grind nuts until they are coarse. Don’t let them become a paste. You want some of the texture of the nuts in your Pastry Cream.
Heat milk over medium high heat until it almost comes to a boil.
While milk heats up, whisk the yolks, sugar and cornstarch for a couple of minutes, until very lightened in color.
Add about 1/3 cup hot milk to yolk mixture. Don’t stop whisking.
Add a little more hot milk and keep whisking.
Finally, add all of the milk and whisk the mixture.
Add cashews and custard mixture back to the saucepan where you heated the milk.
Bring to a boil over medium high heat. Keep stirring with a wooden spoon or spatula, until it comes to a boil and thickens, about 2 minutes.
Pour pastry cream into a bowl. Cover with plastic wrap, directly on the surface of the pastry cream, so it doesn’t form a skin. Refrigerate until ready to use. Pastry Cream will keep in the fridge for up to 3 days.
Salted Caramel Buttercream
For this recipe you may use store-bought caramel if you want to. Just pay attention to the consistency of it and how that’s going to affect the smoothness of your buttercream. If necessary, add more powdered sugar, or more milk by the tablespoon to the buttercream to adjust the consistency. If you’d like to use homemade, here’s a recipe for you.
Start creaming the butter with an electric mixer for about 1 minute. Add caramel sauce to it and beat until creamy and smooth, about 1 minute.
With the mixer off, add all powdered sugar and vanilla in, mix on low until combined. Cream on medium high for 1 minute.
Store buttercream in the fridge for up to 1 week
Salted Caramel Sauce
Warm heavy cream in a small saucepan or in a microwave bowl until it almost comes to a boil.
Place sugar in a medium saucepan. Bring it to a boil over medium heat, while stirring. Once sugar is melted and displays a deep brown color, take it out of the oven, add butter, stir until melted. Add heavy cream, bring it to a gentle boil for about 1 minute.
Remove from heat, add salt and stir until combined. Let sauce cool before using. You can keep it in the fridge for about 20 days. Warm it gently before using. But if you are going to use it in this recipe, use it while room temperature, not cold and not warm either.
Caramelized Nuts
Mix nuts, sugar and butter in a small saucepan. Cook over medium heat until sugar and butter melt and form a thickened caramel that will coat the nuts. Make sure to stir constantly while it cooks. It should take about 4-5 minutes for the caramel to form. Don’t overcook, or you’ll have bitter caramel at the end.
To assemble
With a small spoon, carve a hole on top of the cupcake, about 3/4 inch deep. Fill it with a teaspoon of the Cashew Pastry Cream. Pipe the Salted Caramel Buttercream on top. Top with caramelized cashews! Voila!