CHOCOLATE CUPCAKES

1. Preheat - Preheat the oven to 350°F (180°C) and line a cupcake or muffin pan with 12 liners and set aside.
2. Mix the dry ingredients - In a medium mixing bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
3. Mix the wet ingredients - In a separate large mixing bowl, whisk together the oil and sugars. Then add in the eggs, sour cream, and vanilla extract.
4. Prepare the hot water - In a measuring cup, mix the hot water and espresso together. Slowly pour the hot water into the wet mixture. Whisk until combined.
5. Combine the batter - Using a spatula, add the dry ingredients into the wet ingredients and mix until just combined.
6. Bake - Divide the batter evenly between the cupcake liners (about 3/4 full) and bake for about 15-17 minutes, or until a toothpick comes out with a few moist crumbs. Remove the pan from the oven and let the cupcakes cool for 10 minutes. Then transfer to a wire rack to cool completely.

NUTELLA BUTTERCREAM

1. Beat the butter - In the bowl of a stand mixer fitted with the paddle attachment, or using a hand mixer, beat the softened butter on medium speed until creamy and smooth, about 2-3 minutes.
2. Mix in the other ingredients - Mix in the Nutella, vanilla extract, and salt to the bowl and continue to beat on low speed until well combined, scraping down the sides of the bowl as needed. 
3. Add the powdered sugar - Replace the paddle attachment with the whisk attachment. Gradually add the sifted powdered sugar, about 1 cup at a time, whipping on low speed until fully incorporated before adding more. Adjust the amount of powdered sugar based on your desired sweetness and consistency.
4. Add the cocoa powder - Once all the powdered sugar has been added, add the cocoa powder. Increase the mixer speed to medium and whip the buttercream until light and fluffy, about 2-3 minutes.
5. Mix in the heavy cream - Add the heavy cream and whip until you reach your desired consistency, about 3-5 minutes. Taste the buttercream and adjust the sweetness or flavoring if necessary. 

ASSEMBLY

1. Core each cupcake - Using a cupcake corer or the end of a 1-inch piping tip, core the middle of each cupcake, about 2/3 deep. Fill each cupcake with Nutella filling. 
2. Pipe the first layer - Transfer half of the Nutella buttercream to a piping bag fitted with a medium-sized round piping tip (I used Wilton's 2A tip). Pipe a round buttercream design to each cupcake. It doesn't have to be perfect!
3. Add the hazelnut pieces - On a plate with a few small pieces of chopped hazelnuts at a time, press the frosted cupcake to the plate until completely covered. Do this for all the cupcakes.
4. Pipe another layer - Transfer the other half of the Nutella buttercream to a piping bag fitted with a piping tip of your choice (I used Wilton's 2D tip). Pipe another small layer of this buttercream on top of each frosted cupcake.
5. Garnish - Top with a halved strawberry and Ferrero Rocher chocolate.