Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper.

In a bowl, cream the softened butter with the granulated and brown sugars until smooth and fluffy, about 2 to 3 minutes.

Add the vanilla and mix until combined.

In a separate bowl, whisk together the flour, cocoa powder, and salt.

Gradually add the dry ingredients to the butter mixture, stirring or mixing on low until a thick, pliable dough forms.

Scoop or roll the dough into 1-inch balls and place them on the baking sheet about 2 inches apart.

Press a thumb or the back of a small spoon into the center of each ball to form an indentation.

Bake for 10 to 12 minutes, until the cookies are set at the edges but still slightly soft in the center.

Let them cool completely on the baking sheet.

When cooled, spoon about a teaspoon of chocolate ganache into each indentation. Allow the ganache to set before serving.