Make the ganache: Place chopped chocolate in a heatproof bowl. In a small saucepan, heat the cream until it begins to bubble (but don’t let it boil). Pour the cream over the chocolate. Let sit for 30 seconds, then whisk until smooth. Cool the ganache for about 20-30 minutes, until thickened to a peanut butter-like consistency.
Scoop or pipe teaspoonfuls of ganache onto a parchment-lined baking sheet to form about 24 flat rounds. Freeze the ganache rounds for at least 30 minutes until set.
Prepare the cookie dough: Whisk together flour, cocoa powder, baking soda, and salt. Melt the semisweet chocolate in a double boiler or microwave (using 50% power in 20-second increments). Let cool slightly.
In a stand mixer, beat butter and sugars on medium-high speed for 2-3 minutes until fluffy. Add eggs one at a time, mixing well after each addition. Scrape down the bowl, then mix in vanilla and cooled chocolate.
Gradually add the dry ingredients and mix until just combined. Press plastic wrap on the surface of the dough and refrigerate for 20-30 minutes.
Assemble the cookies: Preheat oven to 350°F. Line two baking sheets with parchment paper. Divide the dough into small balls. Flatten each ball into a pancake shape. Place one frozen ganache piece in the center of a flattened dough ball, then top with another. Seal the edges and roll into a flattened ball or puck shape.
Press the top of each cookie dough ball into sprinkles, then place them on the baking sheet (leave 3-4 inches between cookies).
Bake the cookies: Bake for 9-11 minutes until the tops are puffed and no longer shiny. Use a large round cookie cutter to swirl around each cookie while still soft to make them perfectly round.
Let cool for 10 minutes on the baking sheet before transferring to a wire rack to cool completely.