Ham and Gruyère Thumbprints

1 . Stage

Preheat oven to 400 degrees F. 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.

2 . Stage

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.

3 . Stage

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.

4 . Stage

Remove from oven; press a cheese cube in each indentation. Continue baking until cheese is melted, about 10 minutes. Serve warm.