1-Beat the softened butter until creamy using a stand mixer or electric hand mixer; this step really makes the dough smooth and easy to work with.

2-Add the granulated sugar and light brown sugar, then beat while gradually increasing speed until well combined, about 30-60 seconds; it’s amazing how this blends the flavors.

3-Mix in the large egg yolk and vanilla extract; beat well to incorporate everything evenly, which adds that extra depth of taste.

4-In a separate bowl, whisk together the all-purpose flour, cornstarch, and salt; this dry mix is what gives the cookies their structure.

5-Gradually add the flour mixture to the wet ingredients on low speed until just combined; the dough might be crumbly, so scrape the bowl sides as needed and mix by hand if it helps.

6-Scoop the dough into balls about 1 tablespoon each and roll them smoothly to avoid cracks; for added texture, you can roll them in the optional ½ cup of sugar.

7-Gently press an indent in the center of each ball using your thumb or the back of a rounded teaspoon; then, freeze the shaped balls for 30 minutes to keep their form while baking.

8-Preheat your oven to 375°F (190°C) if you haven’t already, and warm the jam briefly in the microwave until it’s soft but not hot.

9-Fill each indent with the warmed jam, place the cookies 2 inches apart on a parchment-lined baking sheet, and bake for 11 minutes or until the edges are lightly golden.

10-Let the cookies cool completely on the baking sheet before serving; this helps them set and makes them even more delicious.