Make the Dough: Using a hand mixer or stand mixer with a paddle attachment, beat the softened butter on high speed until creamy, about 1 minute. Reduce to medium speed and add the sugar and vanilla, mixing until combined. Scrape the bowl as needed. Add the salt and flour, then mix on low speed until a very soft dough forms. If the dough feels too sticky, mix in 1 additional tablespoon of flour.

Shape the Cookies: Line a baking sheet or plate with parchment or a silicone mat. Scoop about 1 tablespoon (18–20g) of dough per cookie, roll into smooth balls, and place on the sheet. Use your thumb to gently press an indentation into each cookie. If the dough cracks, smooth the edges with your fingers.

Chill: Refrigerate the shaped cookies until firm, at least 4 hours.

Prep for Baking: Preheat oven to 350°F (177°C). Line two baking sheets with parchment or silicone baking mats.

Fill and Bake: Place cookies on baking sheets, spacing 2–3 inches apart (about 12 per tray). Fill each indentation with a scant ½ teaspoon of strawberry jam. Bake for 13–15 minutes, or until the edges are very lightly golden. Let cool on the baking sheet for 5 minutes, then move to a wire rack to cool completely for at least 30 minutes.

Make the Glaze: Whisk the confectioners’ sugar with 1–2 tablespoons of cream (or milk) and vanilla, if using. Add more liquid to thin or more powdered sugar to thicken.

Glaze: Drizzle the glaze over cooled cookies. Allow icing to set for about 1 hour.

Store: Store in an airtight container at room temperature up to 2 days or refrigerated up to 1 week.