Preheat the oven to 350° F. Line cookie sheets with parchment paper, set aside.
In a medium bowl, whisk together the flour and salt, set aside.
In the bowl of a stand mixer beat together the butter and ⅔ cup sugar with the paddle attachment for 3 minutes until light and fluffy.
Add the lemon zest and vanilla and stir. Add the flour mixture a little at a time until it’s incorporated, scrape down the sides as needed.
Place the remaining 2 tablespoons of sugar in a small bowl.
Roll 1 tablespoon of cookie dough into a ball, then roll it in the sugar, and place it on the cookie sheet. Repeat with the remaining cookie dough, placing the cookie balls 2 inches apart on the baking sheet.
Using the round end of a wooden spoon or something similar, and make indentions in the middle of each cookie dough ball about ⅔ of the way down into the dough. They may slightly crack along the edges, that’s okay.
Fill each cookie with a heaping 1/4th teaspoon of jam.
Bake for 13-15 minutes until the cookies look dry on the outside and the bottoms are lightly golden brown. Let the cookies cool on the sheet tray for 5 minutes and then transfer to a wire rack to cool completely.