01 -
In a large bowl (using a stand or hand mixer), whip the butter until it’s light and smooth.
02 -
Toss in the sugars and beat together on medium-high for 30 to 60 seconds. Make sure to scrape the sides of the bowl so everything blends well.
03 -
Mix in the vanilla extract and egg yolk, beating till fully incorporated.
04 -
In another bowl, stir the flour, salt, and cornstarch together. Slowly combine this dry mix with your wet ingredients. The dough will look crumbly—but that’s okay!
05 -
Roll the dough into 1 Tablespoon-sized balls, making them smooth. Coat them in sugar if you want, then use your thumb or a spoon to make a dent in the middle.
06 -
Pop the cookie dough into the freezer and leave it there for half an hour.
07 -
Preheat your oven to 375F (190C). Warm up the jam briefly, so it’s easier to work with. Put a small spoonful into the dent of each cookie.
08 -
Line a baking sheet with parchment and place the cookies 2 inches apart. Cook at 375F for about 11 minutes, or until the edges just start to brown.