Preheat oven to 350°. Grease 6 (½-cup) porcelain ramekins with cooking spray. Place on a rimmed baking sheet.
In a medium bowl, stir together cream cheese, red onion, capers, and bagel seasoning.
In another medium bowl, whisk together eggs, milk, and mustard.
In prepared ramekins, layer the following: 1 bagel chip each, ½ cup spinach, 1 tablespoon cream cheese mixture each, 2 ounces smoked salmon, remaining ½ cup spinach, remaining cream cheese mixture, and remaining 2 ounces smoked salmon.
Pour ¼ cup egg mixture into each ramekin. Let sit for 5 minutes. Tent ramekins with foil.
Bake for 20 minutes. Remove foil, and bake until puffed and set, approximately 15 minutes more. Let cool for 10 minutes.
Using a thin knife, loosen sides of stratas in each ramekin. Invert each ramekin onto a small plate, bagel chip side up. Using a spatula, carefully flip over each strata, bagel chip side down, and transfer to a serving platter.
Garnish with chives, if desired. Serve immediately.
Notes
*We used New York Style Bagel Crisps.
Stratas can be assembled completely, covered, and refrigerated overnight. Tent with foil and bake just before serving.
Recipe by TeaTime Magazine at https://teatimemagazine.com/everything-bagel-stratas-recipe/