Prepare Sundried Tomatoes and Spinach

• Cover sundried tomatoes with boiling water and let sit for 15 minutes. Drain off water.
• Squeeze handfuls of spinach to remove as much water as possible, then chop.

Sauté Vegetables

• Over medium-low heat, heat butter until no longer bubbling.
• Sauté onion until softened and translucent, about 5 minutes.
• Add garlic and stir until golden, about 30 seconds.
• Stir in spinach, roasted red peppers, sundried tomatoes, and 1/4 teaspoon salt. Stir until the mixture is dry, about 1 minute, then remove from heat.

Assemble the Strata

• In a buttered square casserole, layer half of the bread cubes.
• Spread over half of the spinach mixture, then spoonfuls of half of the ricotta.
• Scatter half of the gruyère and parmesan over the mixture. Repeat layering with the remaining ingredients.

Prepare the Egg Mixture

• In a medium bowl, whisk together eggs, milk, cream, mustard, 1/4 teaspoon salt, and pepper.
• Pour the egg mixture evenly over the casserole.

Refrigerate

• Cover with plastic wrap and refrigerate overnight.

Bake

• In the morning, remove the casserole from the fridge and let it sit while preheating the oven to 350°F (175°C).
• Bake the casserole until browned and cooked through, about 45-50 minutes.