01 -
Use a mixer (stand or handheld) to whip butter until light and fluffy.
02 -
Blend the sugars into the whipped butter. Scrape the bowl if needed, and mix until smooth. This should take less than a minute.
03 -
Beat in the vanilla and the egg yolk until fully incorporated.
04 -
Mix salt, flour, and cornstarch in a different bowl. Slowly add it to the wet mix; dough will be crumbly but should hold together.
05 -
Grab about a tablespoon of dough, roll it into a ball, and smooth it out. Coat in sugar (if you want), then use your thumb or a small spoon to press a dent into the middle.
06 -
Pop the cookie balls in the freezer and leave them to firm up for 30 minutes.
07 -
Set the oven to 375°F (190°C). Warm up the jam a little so it's easier to spoon. Fill the indentations in the cookie dough with it.
08 -
Spread cookies on a parchment-covered baking sheet, leaving 2 inches between each. Bake at 375°F for about 11 minutes or until the edges turn golden.