Preheat the oven to 350°F. Lightly grease two baking sheets, or line with parchment.
In a large bowl, beat the butter, sugar, lemon rind or oil, vanilla, and salt until very light.
Beat in the egg.
Add the flour, stirring until well blended.
Use a teaspoon cookie scoop (about 2 measuring teaspoons) or tablespoon cookie scoop (about 4 measuring teaspoons) of dough for each cookie. Scoop cookies onto the baking sheets, leaving 2” between them.
Use your fingertip (for smaller cookies) or thumb (for larger cookies) to put an indentation into the center of each.
Bake the cookies for 12 to 14 minutes. Remove them from the oven.
Let the cookies cool for about 5 minutes to firm up, then move them to a rack to finish cooling.
Once the cookies are cool, fill the indentation with raspberry jam, using about 1/4 teaspoon for each teaspoon-scoop cookie, or 1/2 teaspoon for each tablespoon-scoop cookie.
Yield: 2 1/2 dozen to 5 dozen cookies, depending on size.