This strata is a balance of caramelized onions, cheese and bread baked in a rich custard. You can prepare it in advance for a festive brunch to serve in individual dishes. (If baked in advance you can remove the strata from the dishes for serving, or wrap them and freeze them for breakfast on the go.) This recipe also makes a terrific savory bread pudding side dish for a holiday meal. Individual servings make this humble strata feel special, or see Recipe Notes for baking it in a single dish.
Butter individual ramekins and place them on a baking sheet. Preheat the oven to 350 degrees F.
Whisk the eggs with the cream, milk, garlic, thyme, salt and pepper in a large mixing bowl. Add the bread, caramelized onions, the kale and half of the cheese. Stir well to combine.
Using a spoon to press the bread into the liquid and allow to soak for about 10 minutes. Distribute the mixture into the ramekins and top with the remaining cheese. (You can prepare the recipe in advance up to this point and chill overnight.)
Bake until puffed, golden brown and the liquid in the center is fully set when tested with a table knife, about 30 minutes
To bake this as a single casserole, butter an 8-cup souffle dish. Transfer the mixture into the dish and top with the remaining cheese. Bake until puffed, golden brown and fully set in the center when tested with a table knife, about 50 minutes.