01 -
In a mixing bowl, beat the softened unsalted butter and granulated sugar together until light and creamy.
02 -
Add the egg yolk and vanilla extract to the butter mixture, beating until fully combined.
03 -
Gradually sift in the all-purpose flour and salt, mixing until a soft dough forms.
04 -
Mix in green food coloring until a uniform vibrant green hue is achieved.
05 -
Roll dough into 1-inch balls and arrange spaced apart on a lined baking sheet. Chill for 30 minutes to set.
06 -
Press a thumb into the center of each dough ball to create deep wells for the filling.
07 -
Preheat oven to 350°F. Bake cookies for 25 minutes or until edges are lightly golden. Let cool completely on a wire rack.
08 -
In a small bowl, blend powdered sugar with milk and corn syrup until smooth and glossy.
09 -
Spoon or pipe a small amount of icing into each thumbprint and finish by gently pressing a heart sprinkle into the center. Allow icing to set before serving.