Dress this classic thumbprint cookie, from Dorie Greenspan's book Dorie's Cookies, with an optional drizzle of melted chocolate over the jam center.
Preheat the oven to 350°F. Lightly grease two baking sheets, or line with parchment.
Sift the flour and cocoa together. Set aside.
In a large mixing bowl, beat the butter, sugar, and salt together on medium speed until smooth and creamy. Reduce the speed to low and blend in the egg white and vanilla.
Add the flour mixture in three additions, mixing only until the flour is absorbed before adding more, scraping the sides and bottom of the bowl between additions.
Scoop the dough in generous tablespoonfuls, and roll into balls. A tablespoon cookie scoop works well here. Place on the prepared baking sheet, and make an indentation in the center of each ball with your finger or the end of a wooden spoon handle.
Fill each indentation with raspberry jam.
Bake the cookies for 16 to 18 minutes, or until they feel firm to the touch and the jam is bubbling. Remove them from the oven and cool on the pan for 5 minutes before transferring them to a rack to finish cooling completely.
If you want to drizzle the cookies with chocolate, melt the chips in a bowl over simmering water, stirring until the chocolate is completely smooth. Drizzle over the cookies, then place them in the refrigerator for 30 minutes until the chocolate sets before returning them to room temperature to serve.
Store cookies, well wrapped, at room temperature for several days. Freeze for longer storage.
