Icing:
- 1 cup (120g) confectioners’ sugar
- 1–2 Tablespoons (15–30g/ml) heavy cream, half-and-half, or milk
- Optional: 1/2 teaspoon pure vanilla or almond extract

1. Make the cookies: Using a handheld or stand mixer with a paddle attachment, beat the butter on high speed until creamy, about 1 minute. Switch mixer to medium speed and add the sugar, vanilla, and almond extracts. Scrape down the sides and the bottom of the bowl as needed. Add the salt and flour. Turn the mixer on low and slowly beat until a very soft dough is formed. If the dough seems too sticky for rolling, beat in another Tablespoon of flour.
2. Shape the cookies: Line a baking sheet or plate with a silicone baking mat or parchment paper. Scoop and roll the dough, about a Tablespoon (18–20g) each, into balls, and place on the prepared baking sheet. Press an indentation with your thumb in each ball. The dough may crack slightly when you press your thumb into it. Simply smooth it out with your fingers if you can.
3. Place the baking sheet with the thumbprint cookies in the refrigerator and chill until firm, at least 4 hours.
4. Preheat the oven to 350°F (177°C). Line two baking sheets with parchment paper or silicone baking mats.
5. Place the cookies on the prepared baking sheets, spacing them 2–3 inches apart, about 12 cookies per baking sheet. Fill each cookie with a scant 1/2 teaspoon of jam.
6. Bake the shortbread thumbprint cookies for 13–15 minutes, or until very lightly browned on the edges. The cookies will puff up and spread slightly. Do not overbake. Allow the cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack. Allow to cool for at least 30 minutes before glazing.
7. Make the icing: Whisk the icing ingredients together until smooth. Add more liquid to thin out or add more confectioners’ sugar to thicken to your desired consistency. Drizzle over cookies. Icing will set after about 1 hour.
8. Store cookies in an airtight container at room temperature for up to 2 days, or in the refrigerator for up to 1 week.