Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper. Gather all ingredients, soften the butter, and measure flour and sugar accurately. Prepping everything ahead makes the process smooth.
In a mixing bowl, beat the softened butter and cane sugar until fluffy and light in color, about 5 minutes. Add vanilla and continue mixing until incorporated. This step is key to a tender, airy cookie.
Crack in the large egg and mix until fully combined. The egg binds the dough, giving it structure without making it tough. Make sure to scrape down the sides of the bowl.
Add flour gradually and mix on low speed until a smooth dough forms. Avoid overmixing, as that can make cookies dense. The dough should be soft but hold its shape when rolled.
Divide the dough into 24 balls, rolling each in your hands. Place them evenly on the baking sheets. Press a chocolate heart into the center of each cookie gently to create the classic thumbprint look.
Bake the cookies for 19 minutes or until lightly golden on the bottom. Let them cool completely on the sheet before transferring. The chocolate will settle perfectly as the cookies cool.