In a bowl, whisk together flour, cocoa powder, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream together butter and 3/4 cup sugar until light and fluffy. Scrape the bowl and mix in egg yolks and vanilla extract.
Add the dry ingredients in 3 additions, scraping the bottom and sides of bowl between each addition. Refrigerate for 30 minutes.
Preheat oven to 350 degrees F with racks in the upper and lower thirds of the oven. Line two baking sheets with parchment or nonstick baking mats.
Scoop dough into 1-1/2 teaspoon portions (I use a small cookie scoop) and roll between your hands into a ball. Place a few tablespoons of granulated sugar in a shallow dish and roll the dough balls in the sugar to coat.
Place dough onto the prepared baking pans. Using your finger or the back of a 1/4 teaspoon measuring spoon, make an indentation in the center of each cookie.
Bake for 13-15 minutes, rotating pans halfway through, until cookies are set. Remove from the oven and use the back of a 1/2 teaspoon measuring spoon to gently re-press the indentations. Let cookies stand on the baking sheets for 5 minutes before transferring to wire racks to cool completely.
Use a spoon or a piping bag, fill each indentation with about 1 teaspoon of chocolate hazelnut spread. Top with a raspberry (cut in half if large) and serve.
The cookies should be filled with chocolate hazelnut spread and topped with a raspberry the day of serving. You can bake the cookies and store them at room temperature, unfilled, up to 3 days in advance in a tightly-covered container.