2 tablespoons extra-virgin olive oil, plus more to grease and drizzle
1/2 cup French Onion Salt or 1-ounce packet French onion dip mix
2 cups dairy, almond, or oat milk
6 eggs, beaten well
4 cups day-old ½-inch whole grain bread cubes
1/3 cup grated Gruyère cheese
1 bunch chives, minced
Rub a small splash of olive oil across an 8-inch baking dish, or equivalent.
In a medium bowl, whisk together the oil, onion dip mix, and milk. Add the eggs and whisk well again. Arrange the bread cubes in the prepared baking dish in an even layer. Very slowly, drizzle the liquid mixture over the bread and sprinkle with the cheese. Cover the dish and refrigerate overnight.
When you are ready to bake, preheat the oven to 350°F and place a rack in the center. Bake the strata, uncovered, for 45 to 55 minutes, until the egg is set and puffy and the edges are golden brown. Cut into it to be sure it is well cooked.
Serve the strata warm, drizzled with a bit of olive oil and sprinkled with chives.