Chocolate Thumbprints

Preheat oven to 350°F.

Prepare Chocolate Dough:

Beat butter and sugar with a stand mixer fitted with a paddle attachment on medium speed until light and fluffy, about 2 minutes, stopping to scrape down sides as needed. Add egg yolk, vanilla, and cream; beat on medium speed until combined, about 15 seconds.

Whisk together flour, cocoa, baking powder, espresso granules, and salt in a medium bowl until well combined.

With mixer on low speed, gradually add flour mixture to butter mixture, beating until combined, 30 seconds to 1 minute, stopping to scrape down sides as needed. Use dough immediately, or wrap tightly in plastic wrap, and refrigerate for up to 24 hours. Let dough stand at room temperature until softened before using, about 30 minutes to 1 hour.

Place sprinkles in a small bowl. Scoop and roll dough into 1-tablespoon balls; roll in sprinkles until evenly covered, and place about 3/4 inch apart on a parchment paper-lined baking sheet. Make an indentation in center of each ball using back of a 1/2-teaspoon scoop. Smooth any cracks in edges.

Bake in preheated oven until tops appear dry, 8 to 10 minutes. Remove from oven, and gently press down centers with 1/2-teaspoon scoop. Let cool completely on baking sheet on a wire rack, about 30 minutes to 1 hour.

Prepare Cookie Glaze:

Stir together powdered sugar, corn syrup, vanilla, salt, and 3 tablespoons of the milk in a medium bowl until combined. Stir in up to remaining 1 tablespoon milk, 1/2 to 1 teaspoon at a time, until desired consistency is reached.

Divide 1/2 cup Cookie Glaze evenly among 3 small bowls; stir red and green food coloring gels separately into 2 of the bowls, adding more to reach desired shades. Leave third bowl plain.

Spoon or pipe glazes into indentations in centers of cooled thumbprints as desired. Let stand until mostly set before serving, 1 to 2 hours. Store in an airtight container at room temperature for up to 5 days.