Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the vanilla extract.
Sift together the flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Roll tablespoons of dough into balls and place them on the prepared baking sheets about 2 inches apart. Flatten each ball slightly with the palm of your hand.
Bake in the preheated oven for about 8-10 minutes, or until the edges are set.
Remove from the oven and let cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
While the cookies are cooling, prepare the ganache. In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer.
Remove from heat and pour over the chocolate chips in a medium bowl. Let it sit for 1-2 minutes, then stir until smooth and glossy.
Allow the ganache to cool slightly at room temperature, then cover and refrigerate for about 15 minutes until it thickens, stirring occasionally.
Once the cookies are completely cool, spread a generous amount of ganache on the bottom of one cookie and top with another to form a sandwich. Repeat with the remaining cookies.
If desired, roll the edges of the cookies in sprinkles for added decoration.