Effortless Thumbprint Cookies (Print Version)

# Ingredients:

01 - 1 stick (226g) unsalted butter, softened so it's easy to mix.
02 - 1/3 cup (70g) packed light brown sugar.
03 - 1/3 cup (70g) granulated sugar.
04 - 1 large egg yolk, separated from the white.
05 - 3/4 teaspoon vanilla extract for flavor.
06 - 2 1/4 cups (280g) plain all-purpose flour.
07 - 2 teaspoons of cornstarch.
08 - 1/2 teaspoon salt for balance.
09 - 1/2 cup sugar for coating (optional).
10 - 1/3 cup (105g) of your favorite jam or preserves.

# Instructions:

01 - Using a stand mixer or electric hand mixer, whip the butter in a big bowl until it's light and airy.
02 - Mix in both sugars, scraping the bowl sides, and beat on medium speed for 30-60 seconds until smooth.
03 - Toss in the egg yolk and vanilla extract and blend it all thoroughly.
04 - In another bowl, stir together the flour, salt, and cornstarch. Slowly add this to the butter mixture until it forms a crumbly dough.
05 - Form the dough into 1-Tablespoon balls, rolling until smooth. If you'd like, roll them in sugar. Use your thumb or a small spoon to press an indent in the center.
06 - Pop the dough balls into the freezer for half an hour to firm up.
07 - Preheat oven to 375F (190C), then gently heat up the jam so it spreads easily. Spoon it into the indents.
08 - Line a baking sheet with parchment paper, place cookies 2 inches apart, and bake at 375F for around 11 minutes. The edges should just be turning golden.

# Notes:

01 - Roll the balls completely smooth to keep them from cracking.
02 - Feel free to pick any jam or preserves you like.
03 - Let the cookies cool fully on the tray before moving them.