Prepare a large bowl with water and ice cubes to create an ice bath. Set aside.

Bring a large pot of water to boil. Add the broccoli florets and blanch for 2 minutes. Remove broccoli from boiling water and add them to the ice bath immediately.

Once all the broccoli has cooled in the ice bath, drain the water and set the broccoli in the bowl aside.

Spray a large skillet lightly with nonstick olive oil cooking spray. Place the pan over medium-high heat.

Add the onions and cook until translucent. Add the sausage, cooking until browned and no longer pink, breaking up the sausage as it cooks.

Remove the sausage onion mix to a paper towel lined plate. Set aside.

Spray a 9x13-inch baking dish with nonstick olive oil cooking spray.

Add half the cubed bread pieces to the prepared dish.

Sprinkle half the cheese, half the broccoli and half the sausage.

Add the rest of the bread and sprinkle remaining cheese, broccoli and sausage over the top.

In a large bowl, whisk together eggs, heavy cream and milk until well combined.

Add the salt, ground mustard and black pepper. Whisk again to incorporate.

Pour the egg mixture over the bread mixture slowly, allowing it to be absorbed a bit to prevent overflowing.

Press the bread down into the mixture as necessary to allow it all to be covered.

Cover baking dish with plastic wrap and refrigerate overnight or at least 8 hours.

Preheat oven to 350°F.

Uncover baking dish and bake strata in the center of preheated oven for approximately 1 hour 30 minutes, until the top is golden and a knife inserted in the center comes out clean.