Preheat oven to 375°F (190°C). Draw 24 (1½-inch) circles at least 1½ inches apart on 2 sheets of parchment paper. Place prepared parchment, ink side down, on rimmed baking sheets.

In a medium saucepan, bring butter, ½ cup (120 grams) water, milk, sugar, and kosher salt to a rolling boil over medium-high heat. Add flour, and stir with a wooden spoon until combined. Cook, stirring constantly, until a skin forms on bottom of pan and mixture pulls away from sides of pan and forms a ball, 1 to 2 minutes.

Transfer mixture to the bowl of a stand mixer fitted with the paddle attachment; beat at medium-low speed until dough cools slightly and is no longer steaming, 2 to 3 minutes. Add eggs, one at a time, beating until combined after each addition. (Batter will be shiny and thick.) Fold in cheese and bacon.

Transfer batter to a large pastry bag fitted with a medium round piping tip (Ateco #806). Holding bag perpendicular to parchment and about 1½ inch above, slowly pipe into 1- to 1½-inch-tall mounds. Using a wet finger, smooth pointed tops if necessary. Sprinkle with sea salt (if using).

Bake, one pan at a time, for 10 minutes. Rotate pan, and bake until fully puffed and deep golden brown, 5 to 8 minutes more. (Let remaining pan stand at room temperature until ready to bake.) Let cool completely on pans. Refrigerate in an airtight container for up to 3 days.