Meanwhile whisk milk, eggs, 1 teaspoon salt and several grinds of pepper until smooth.
Line pan bottom with half the bread slices to form a tight fit. Scatter half of the squash, kale, and cheese over the bread. Pour 2 cups of egg mixture over the topped bread. Make another layer with remaining bread, scattering with remaining squash, kale and cheese. Slowly pour remaining egg mixture over bread. Let stand, occasionally pressing on bread to submerge it, until it has absorbed the milk mixture, at least 15 minutes. (Can be covered and refrigerated overnight.)
Adjust oven rack to middle position and heat oven to 325 degrees. Bake until custard is set, about 50 minutes. Without adjusting oven rack, turn on broiler; broil until strata is spotty brown and puffy, about 5 minutes longer.
Remove from oven, let stand for 8 to 10 minutes, and then serve immediately.
Notes
You can make strata with milk, but you might want the richer half and half for your more celebratory holiday brunch.
Recipe by Three Many Cooks at https://threemanycooks.com/recipes/strictly-vegetarian/butternut-squash-and-kale-strata/