Blackened Spinach Bread Pudding

Ingredients

• Two 10-ounce packages of chopped frozen spinach, or a bit more than two pounds of fresh spinach leaves, washed and trimmed
• 1/4-1/3 cup olive oil
• 1 1/2 pounds of cremini or button mushroom caps, sliced (use the stalks for stock or duxelles*)
• 2 Tbsp onion slices, crumbled, or 1/2 cup finely chopped sautéed onion
• 1 Tbsp Blue Grass N12
• 1/2 tsp freshly grated nutmeg
• 1 tsp salt
• 1 Tbsp butter, plus more for the pan
• 1 cup whole milk (or non-dairy milk if you like)
• 8 eggs
• 6 thick slices of challah or brioche, torn or chopped into large pieces