Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large mixing bowl, cream together the butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg yolk and vanilla extract until fully incorporated.
In a separate bowl, whisk together the flour, cocoa powder, and salt.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Using a cookie scoop or spoon, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Use your thumb or the end of a wooden spoon to make an indentation in the center of each cookie.
Bake for 10-12 minutes, or until the edges are lightly golden and the centers are set.
Remove the cookies from the oven and immediately place a few chocolate chips in each indentation.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Once the cookies are completely cool, melt the raspberry jam in a microwave-safe bowl for about 30 seconds.
Drizzle the melted jam over the chocolate-filled indentations of each cookie.
Sprinkle chopped nuts over the top of each cookie, if desired.