In a large skillet over medium-high heat, melt the butter. Add the onion and a pinch of kosher salt and cook, stirring, until soft, about 10 minutes. Add the garlic and cook for another minute.
Stir in the flour to evenly distribute. Add 1 cup milk, stirring continuously until thickened; repeat with the remaining 1 cup. Stir in the chicken soup bouillon, then add the chicken, thyme and a few turns of black pepper and simmer, stirring often, until the chicken is cooked through and no longer pink, 10 to 15 minutes. Add the artichokes, spinach, cream cheese, parsley, a pinch of crushed red pepper and a few turns of black pepper. Stir until the cream cheese is melted. Taste and adjust as desired.
Divide the spinach, artichoke and chicken mixture into eight 5-inch aluminum pans or a 9-by-13-inch casserole pan. Separate the biscuits, then top the casseroles with them. Brush them with the egg wash and sprinkle with the flaky salt and some black pepper.
If baking immediately, preheat the oven to 400 degrees F. Bake until the biscuits are golden brown, about 15 minutes.
If freezing, allow the casseroles to cool to room temperature, then cover tightly with foil and freeze. To reheat, bake at 400 degrees F for 30 minutes.