Grease a 9x13-inch baking pan with cooking spray and set aside.
Remove the crust and cut the 27 ounces sandwich bread into 1-inch cubes; do not use the end pieces. Each slice should turn into 9 cubes. We use King's Hawaiian Bread, but you can use regular white bread; you'll need about 26 slices. Add the cubed bread to a large mixing bowl and set aside.
Add 1 pound ground breakfast sausage to a large skillet over medium-high heat and cook it through.
Pour ⅓ cup 100% pure maple syrup over the sausage and cook for 1 to 2 additional minutes before transferring to the large mixing bowl with the bread.
Reduce heat to medium, add 4 tablespoons salted butter, 4 sprigs fresh thyme, and the chopped 1 yellow onion, and sauté until the onions are soft and translucent about 5 minutes.
Add 1 tablespoon garlic paste and cook for 1 additional minute, stirring frequently so the garlic doesn't burn. Discard the sprigs of thyme.
Transfer to the mixing bowl and add 8 ounces shredded cheddar cheese and ½ cup chopped fresh parsley and stir/toss to combine.
Transfer the bread and sausage mixture to the prepared baking dish and gently press the mixture down into the pan so it's nice and even.
In a separate bowl or large measuring cup, beat together 6 large eggs, 2 cups half & half, 1 teaspoon sea salt, and ¼ teaspoon ground black pepper with a fork.
Pour the egg mixture over the bread mixture in the pan.
Cover the pan and refrigerate for at least 2 hours, preferably overnight.
When ready to bake, preheat the oven to 350°F.
Bake the strata for 40 to 50 minutes until it has puffed up slightly and the top is beginning to turn golden brown.
Slice and serve immediately. Feel free to serve with additional syrup.