Preheat your oven to 350 degrees F. Fill a cupcake tin with cupcake liners and set aside.
In a large mixing bowl, use an electric hand mixer cream together the butter and granulated sugar until the butter is mostly incorporated with the sugar. There can be a few clumps of butter in the mixture.
Add the eggs, milk, and vanilla. Mix again on medium-high speed until the eggs are homogenous with the creamed butter mixture.
Add the Nutella and mix again for 1 minute until incorporated.
Add the baking powder, flour, and cocoa powder. Mix on medium speed until the dry ingredients are just incorporated into the batter and the mixture is (mostly) smooth.
Divide the batter among the cupcake liners and bake the cupcakes for 20 minutes.
Remove the cupcakes from the oven. Let cool for a few minutes then remove to the wire cooling rack.
Slice the strawberries in half and place them in a small saucepan with the granulated sugar over medium heat. Stir until mushy and remove from the heat to cool.
Once the strawberry mixture is cool, combine it with the powdered sugar and butter. Whisk on medium speed with an electric hand mixer until smooth and creamy.
Add the frosting to a piping bag with the tip of your choice. Divide evenly on top of the cupcakes.