4 ounces unsalted butter, at room temperature
4 ounces Nutella
1/4 cup granulated sugar
3/4 cup packed light brown sugar
1 large egg, at room temperature
1 1/2 teaspoons vanilla extract
1-1/4 cups all-purpose flour
3/4 teaspoon baking soda
3/4 teaspoon salt
For the Fudge Filling:
8 ounces dark or semi-sweet high quality chocolate, chopped into small pieces
8 ounces sweetened condensed milk
1/4 teaspoon salt
1/2 cup pistachios, shelled and roughly chopped
In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl using a handheld mixer cream the butter, Nutella, and sugars until well combined; about 2 minutes. Beat in egg and vanilla.
In a separate bowl combine the flour, baking soda and salt. Gradually add it to the creamed mixture and mix until combined. Chill for 1 hour.
Preheat oven to 325 degrees (F) 30 minutes before baking.
Grease 2 (12 mold) mini muffin tins; set aside.
Shape chilled dough into 24 small balls, each a little less than 1 inch in size.
Place balls in prepared pans.
Bake in preheated oven for 14 minutes. Cool cookie cups in pans for 5 minutes before removing to wire racks to cool completely.
For the filling:
Place chopped chocolate in a small microwaveable bowl and heat on low in 20 second increments - stirring in between - until chocolate is completely melted; stir in condensed milk and salt; whisk until smooth.
Fill each cookie cup with a scant tablespoon of the filling. Sprinkle with pistachios.
*The cookie cups should sink in the center after being removed from the oven. If by chance one or two don't, simply press the center down gently with the back of a spoon. This will ensure there's room for the filling.
*The cookie cups will be very soft when removed from the oven. Allow them at least 5 minutes in the pan to firm up. Once cooled they'll become crunchy.