Preheat your oven to 350°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside. Fit a large piping bag or large zip-top plastic bag with an open star piping tip and set it aside as well.

In a large bowl with a handheld mixer or stand mixer with the paddle attachment, place the butter and whip until light and fluffy (about 5 minutes). Add the cornstarch, confectioners’ sugar, and then the flour, xanthan gum and salt, beating until well-combined after each addition. After adding the final ingredient, turn the mixer speed up to high and continue to beat for another 5 minutes uninterrupted. After adding the flour, the mixture will first seem a bit crumbly and then will turn into a lovely whipped mixture that looks a bit like frosting.

Transfer the cookie into the piping or plastic bag fitted with the open star tip, and pipe shapes about 1 1/2-inches in diameter onto the prepared baking sheet, about 1 inch apart. With a wet pointer finger, create a divot in the center of each cookie. Fill the center with a small dollop of jam. Place the baking sheet in the refrigerator for about 10 minutes or the freezer for about 3 minutes, until the cookies are firm.

Place the baking sheet in the center of the preheated oven and bake until the edges of the cookies are just beginning to brown, at least 13 minutes for small cookies. Allow the cookies to cool completely on the baking sheet.