Preheat the oven to 350 degrees F. Spray the cups of a standard-size muffin tin with nonstick cooking spray. Set aside.
In a medium bowl, mix together the flour, cocoa powder, salt, and baking soda. Set aside.
With a hand mixer, beat together the butter, sugar, and brown sugar until light and fluffy, about 2-3 minutes. Add the egg and vanilla and mix until well combined. Slowly add the dry ingredients to the wet ingredients, mixing on low speed until incorporated.
Using a cookie scoop (about 1 1/2 TBSP), scoop the cookie dough into the prepared muffin tin cups, dividing the dough evenly. Press the cookie dough into the bottom of each cup and about halfway up the sides. (I use a measuring spoon for this.) Bake for 11 to 13 minutes.
Remove from oven. Use the back of the cookie scoop or measuring spoon to press down on the center of each cookie to form the cup shape.
Allow the cookie cups to cool for 15 minutes in the pan. Then transfer them to a wire rack to cool completely.
Chocolate Frosting
Melt chocolate chips in a glass bowl in the microwave by heating for 30 seconds and then stirring. Repeat until melted. Let cool for 3-5 minutes. (Don't let it solidify.)
With a hand mixer, beat together the cream cheese and butter on medium speed for about 3 minutes. Slowly add in the sugar, cocoa powder, vanilla, and salt. Mix until well combined.
Add the melted chocolate and mix until just combined. Beat on medium-high speed for 1 minute. If the frosting is too thick, add a teaspoon of milk and mix. Repeat until you're desired consistency is reached.
Transfer the frosting to a piping bag fitted with a tip. Pipe the frosting into cups and garnish each one with a raspberry. Serve immediately.
Notes
You can also use a food storage bag with the corner cut off to pipe the frosting into the cups.
For a little extra garnish, you can add a piece of dark chocolate in the frosting on top of each cup with the raspberry.