Step 1

Pour water into a large skillet to come ½" up the sides; bring to a simmer over medium heat. Generously grease four 8-oz. ramekins or small heatproof bowls (about 1 tsp. each) with unsalted butter; sprinkle generously with kosher salt and freshly ground pepper. Divide 4 Tbsp. finely chopped chives among ramekins.

Step 2

Crack 1 large egg into each ramekin, then transfer ramekins to skillet and cover skillet with a lid. Cook eggs, adjusting heat as needed to maintain a simmer, until whites are set and yolks are still soft, 4–7 minutes. Using tongs, carefully transfer ramekins to plates.

Step 3

Divide 4 Tbsp. heavy cream (if using) among ramekins; season lightly with more salt and pepper. Serve eggs with warm buttered toast.