1. Adjust oven rack to middle position and heat oven to 500°F. Cook bacon in medium saucepan over medium heat until crisp, about 10 minutes. Transfer bacon to paper towel lined plate. Add leeks and cook, stirring occasionally, until softened, about 10 minutes. Transfer leeks to plate with bacon.

2. Melt butter in now-empty pan over medium heat. Stir in flour and cook, stirring constantly, for 1 minute. Gradually whisk in half-and-half; bring mixture to boil, whisking constantly. Simmer, whisking frequently, until thickened, 2 to 3 minutes. Remove pan from heat, and stir in bacon-leek mixture, Gruyère, 3/4 teaspoon salt, 1/2 teaspoon pepper, mustard, nutmeg, and cayenne.

3. Lightly spray six 6-ounce ramekins with oil spray. Evenly divide bacon-leek filling among ramekins. Using back of spoon, push filling 1 inch up sides of ramekins to create 1/8-inch-thick layer. Shape remaining filling in bottom of ramekin into 1 1/2-inch diameter mound, making shallow indentation in center of mound large enough to hold yolk. Place filled ramekins in 13 x 9-inch glass baking dish. Bake until filling just starts to brown, about 7 minutes, rotating dish halfway through baking.

4. While filling is heating, crack eggs (taking care not to break yolks) into individual cups or bowls. Remove baking dish with ramekins from oven and place on wire rack. Gently pour eggs from cups into hot ramekins, centering yolk in ramekin. Spray surface of each egg with oil spray and sprinkle each with pinch salt. Return baking dish to oven and bake until whites are just opaque but still tremble, 6 to 8 minutes, rotating dish halfway through baking.

5. Remove baking dish from oven, and using tongs, transfer ramekins to wire rack. Let stand until whites are firm and set (yolks should still be runny), about 10 minutes. Serve immediately.

Serves 6