Preparation

Make the cookies:

• In a medium bowl, whisk the flour with the cream of tartar and salt until well blended. With a stand mixer (use the paddle attachment) or a hand mixer, beat the butter, sugar, and confectioners’ sugar in a large bowl on medium speed until light and fluffy, about 4 minutes, scraping the bowl as needed. Add the egg, vanilla extract, and almond extract and beat until blended. Add the flour mixture and mix on low speed until just blended.
• On a lightly floured surface, divide the dough into six equal pieces. If the dough is very soft, wrap each portion in plastic and refrigerate until firmer, about 1 hour.
• Heat the oven to 350°F and have ready two large ungreased baking sheets (or line them with nonstick baking liners). If the dough is in the refrigerator, remove it and unwrap it. Using your hands or a rolling pin (or both), shape each piece into a flat 12×1-1/2-inch strip about 1/4 inch thick, dusting with flour if needed. Transfer the strips to the prepared baking sheets, spacing them about 3 inches apart.
• Using the butt end of a knife handle dipped lightly in flour, make an indentation down the middle of each strip (this will widen the strip to about 1-3/4 inches and make a depression about halfway down into the strip). Spread 1 Tbs. of the jam evenly down the indentation of each strip.
• Bake until the cookie strips are lightly browned on the bottom and edges, about 20 minutes. Let the strips cool on the sheets on racks for 5 minutes before carefully transferring them to racks to cool completely (a long offset metal spatula is good for this). Before glazing, set the rack over a baking sheet or a sheet of waxed paper. If you plan to freeze these cookies, do it before glazing.

Glaze the cookies:

• In a small bowl, mix the confectioners’ sugar with the salt, water, and almond extract. The glaze should be thick enough to hold its shape when drizzled; add more confectioners’ sugar or water if needed. Using the tines of a fork, drizzle the glaze over the tops of the cooled cookie strips. (Or transfer the glaze to a sturdy zip-top plastic bag, snip off a tiny bit of one corner of the bag and drizzle.) Leave the cookies on the rack until the glaze is set, about 30 minutes, and transfer to a cutting board. With a serrated knife, cut each bar on the diagonal into 1-inch-thick diamond shapes.
• Store at room temperature or freeze (unglazed) in an airtight container, separating the cookie layers with waxed paper.