Ham and Gruyere Thumprints

(from Martha Stewart Living Magazine)
½ cup (1 stick) unsalted butter, cut into large pieces
½ teaspoon coarse salt
1 cup all-purpose flout
4 large eggs
½ teaspoon freshly ground pepper
½ cup finely chopped or ground Black Forest Ham (2 oz)
1 cup finely shredded Gruyere cheese, plus 36 ½-inch cubes for centers (8 oz total)
Preheat oven to 400F. Bring butter, salt, and 1 cup water to a boil in a large, heavy saucepan over medium heat, stirring occasionally (butter will melt). Add flour; stir vigorously until incorporated. Continue to cook, stirring, until the mixture pulls away from the sides and a thin film forms on bottom of pan, 1 to 2 minutes. Remove from heat; let cool 2 minutes.
Transfer dough to a large bowl; add eggs one at a time, beating with a wooden spoon to incorporate each egg before adding the next, about 2 minutes. Stir in pepper, ham, and shredded cheese.
Spoon dough into a pastry bag fitted with a ½-inch star tip. On a baking sheet lined with parchment paper (or a Silpat mat), pipe 1 ½-inch-wide rosettes, 1 inch apart. Make a deep indentation in the center of each with your thumb (dampen thumb to keep it from sticking to dough). Bake until crisp and golden, 25 to 30 minutes. Transfer thumbprints to a wire rack to cool completely. Press a cheese cube into indentation of each.
Place on clean baking sheets; freeze (uncovered) until firm, about 1 hour. Transfer to an airtight container; freeze until ready to use, up to 6 weeks.
To serve, preheat oven to 425F. Place thumbprints on ungreased baking sheets; bake until heated through and cheese is melted, 10 to 14 minutes. Serve warm. Makes 3 dozen.
*NOTE: I love this recipe because you can make it in advance and keep it in the freezer for drop-in or unexpected guests. Great for the holiday season!