Preheat the oven to 350°F / 175°C and place 12 cupcake liners in a cupcake pan.

Add 3/4 cup milk, 1/3 cup chocolate chips, and 1 tsp instant espresso powder into a heat proof bowl. Heat in the microwave at power level 8 for 1 minute or over a double boiler until the chocolate has melted.

Whisk together until the ingredients have combined, making sure all the chocolate is melted.

Sift 3/4 cup all purpose flour, 3/4 cup granulated sugar, 1/3 cup cocoa powder, 1/2 tsp baking soda and 1/2 tsp salt into chocolate espresso mixture and stir until combined.

Scrape the sides and bottom of the bowl as needed with a spatula.

Add 2 large eggs, 1/3 cup vegetable oil, 1 tsp vinegar and 1 tsp vanilla. Mix just until the batter is smooth.

Fill cupcake liners 3/4 full and bake for about 17-18 minutes or until a toothpick comes out with a few moist crumbs.

Allow the cupcakes to cool for 5 minutes in the pan before moving them to a cooling rack to finish cooling.

While the cupcakes cool make the fluffy Nutella buttercream. Beat 1/2 cup of unsalted butter on a medium speed for 30 seconds with a paddle attachment or hand mixer until smooth. 

Mix in 1/4 cup Nutella, 1/2 tsp vanilla extract and 1/4 tsp salt on a low speed.

Slowly add in 1 1/2 cup powdered sugar, followed by 1/4 cup cocoa powder. Scrape the sides and bottom of the bowl as need with a rubber spatula.

Add 2 Tbsp of heavy cream half through adding in the powdered sugar to make it easier to mix.

Beat on low until the ingredients are fully incorporated and the desired consistency is reached.

If the frosting is too thick, add an extra Tbsp of heavy cream. If it's too thin, add in another 1/4 cup of powdered sugar.

Stir by hand with a rubber spatula to get the frosting SUPER smooth. Place into a large piping bag fit with a Wilton 1M frosting tip.

To decorate these Nutella cupcakes, first remove the center of each cupcake and fill with a spoonful of Nutella.

Pipe a large swirl of Nutella buttercream on top of each cupcake with a Wilton 1M frosting tip.

Drizzle some Nutella over the top of each cupcake and sprinkle with toasted hazelnuts if desired!