01 -
Preheat oven to 350°F and line two baking sheets with parchment paper.
02 -
In a large bowl, cream butter, granulated sugar, and brown sugar for 2 to 3 minutes until pale and fluffy.
03 -
Mix in egg and egg yolk until smooth, then stir in vanilla extract and espresso powder if using.
04 -
In a separate bowl, whisk together flour, cornstarch, baking soda, baking powder, and salt.
05 -
Add dry ingredients to wet mixture and stir just until dough forms with no visible flour streaks.
06 -
Chill dough for 30 minutes to ensure thicker, softer cookies and easier filling.
07 -
Divide dough into 16 portions (about 2 tablespoons each). Flatten each portion, place chocolate truffle or square in center, then wrap dough around it, sealing edges completely.
08 -
Place filled dough balls seam-side down on prepared sheets, spacing them adequately.
09 -
Bake for 10 to 12 minutes until edges are lightly golden and tops are set but still soft and slightly underbaked in the center.
10 -
Allow cookies to cool on the pan for 10 minutes to set exterior while maintaining a tender interior. Optionally, sprinkle flaky sea salt while warm. Serve warm for optimal center melt.