Ingredients

1/2 cup (1 stick) unsalted butter, cut into large pieces
1/2 teaspoon coarse salt
1 cup water
1 cup all-purpose flour
4 large eggs
1/2 teaspoon freshly ground pepper
1/2 cup finely chopped or ground Black Forest ham (2 ounces)
1 cup finely shredded Gruyere cheese, plus 36 cubes (1/2 inch) for centers (8 ounces total)

Directions

1. Preheat oven to 400 degrees.
2. Bring butter, salt, and the water to a boil in a large, heavy saucepan over medium heat, stirring occasionally. Add flour; stir vigorously until incorporated. Continue to cook, stirring, until the mixture pulls away from sides of pan and a thin film forms on bottom of pan, 1 to 2 minutes. Remove from heat; let cool 2 minutes.



3. Transfer dough to a large bowl; add eggs 1 at a time, beating with a wooden spoon to incorporate each before adding the next, about 2 minutes. Stir in pepper, ham, and shredded cheese.



4. Spoon dough into a pastry bag fitted with a 1/2-inch star tip. On baking sheets lined with nonstick baking mats or parchment paper, pipe rosettes (each 1 1/2 inches wide), 2 inches apart. Make a deep indentation at the center of each with your thumb (dampen thumb to keep it from sticking to dough). Bake, rotating sheets halfway through, until crisp and golden, 25 to 30 minutes.
5. Remove from oven; press a cheese cube in each indentation. Continue baking until cheese is melted, about 10 minutes. Serve warm.

Makes 3 dozen.

Make ahead: The thumbprints can be partially prepared ahead and then frozen. Form and bake thumbprints as directed in steps 1 to 4. Transfer to wire racks to cool before inserting cheese cubes; place on clean baking sheets, and freeze until firm, about one hour, before freezing in airtight containers, up to six weeks. To serve, remove from freezer and bake (without thawing) in a 425-degree oven for about 15 minutes.

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