Melt 2 tablespoons butter in a large skillet over medium heat. Add onions and mushrooms. Saute until soft, approximately 5 minutes. Add in spinach/kale and basil along with 1 tablespoon water. Season with salt and pepper. Stir until greens are wilted, approximately 2 minutes for spinach and 4 minutes for kale. Set aside to cool.
Heat a medium non-stick skillet over medium-high heat. Break the maple sausage into small chunks and cook until browned. [If sausage is in links, remove the sausage from their casings]. Drain on a paper towel once browned.
In a large bowl, whisk eggs until well combined. Mix in the half-and-half. Season with salt and pepper.
Grease a 9x13 dish. Cut bread into 1" cubes and layer half of the bread to cover the entire bottom of the pan. Spread the vegetable mixture over the bread and top with 1/2 of the cheese. Layer the remainder of bread on top of the vegetables and cheese layer. Top with sausage crumbles and remainder of cheese.
Pour the egg mixture over the entire dish. Press lightly on any areas where the bread is not submerged in the egg mixture. Cut the cold butter into small cubes and spread the cubes evenly over the top of the strata.
Cover and refrigerate overnight or at least 2 hours.
Preheat the oven to 350 degrees. Place the baking dish in a larger roasting pan and fill the pan with hot water half way up the side of the baking dish.
Bake 50-60 minutes or until top is slightly browned. Let stand 5 minutes before cutting.
You can sub the half-and-half for whole or even 2% milk. It just wont' be quite as rich.
I know this recipe says to cover and refrigerate for at least two hours to let the bread absorb the egg mixture, but I have baked this immediately before and had it turn out just slightly different -- not enough to not make it if you are in a hurry.