Thumbprint Cookies

Adjust oven racks to upper-middle and lower-middle positions and heat oven to 350 degrees. Line 2 baking sheets with parchment paper. Whisk flour, salt, baking soda, and baking powder together in medium bowl; set aside.

Using stand mixer fitted with paddle, beat butter and ⅔ cup sugar on medium speed until fluffy, 3 to 6 minutes, scraping down bowl as needed. Add cream cheese, egg, and vanilla and beat until evenly combined, about 30 seconds. Reduce speed to low, slowly add flour mixture, and mix until fully incorporated.

Spread remaining ⅓ cup sugar evenly in shallow dish. Working with 1 tablespoon dough at a time, roll dough into 36 balls. Drop dough balls into sugar and roll to coat. Stagger dough balls evenly on prepared sheets. Using greased rounded 1-teaspoon measuring spoon, make indentation in center of each dough ball. Gently pinch together any large cracks around edges of cookies.

Bake cookies until just beginning to set, about 10 minutes, switching and rotating sheets halfway through baking. Transfer baking sheets to wire racks (do not turn off oven). Gently reshape indentation in center of each cookie with greased rounded 1-teaspoon measure.

If using jam, place jam in 1-cup liquid measuring cup or microwave-safe bowl and microwave until loose and bubbling around edges, about 30 seconds. (If using curd, do not reheat.) Carefully fill each indentation with 1 teaspoon warmed jam or chilled curd.

Return cookies to oven and bake until cookies are beginning to turn golden around edges, about 8 minutes, switching and rotating sheets halfway through baking. Let cookies cool on sheets for 5 minutes, then transfer cookies to wire racks. Let cookies cool completely before serving, about 20 minutes. (Cookies can be stored in airtight container at room temperature for up to 3 days.)