Egg Bhurji Strata

Name: Egg Bhurji Strata
Ingredients: 2 Tbsp. unsalted butter, plus more for pan; 7 large eggs; 1¾ cups whole milk; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; Freshly ground black pepper; 2 tsp. vegetable oil; ½ tsp. cumin seeds; 2 large leeks, white and pale green parts only, thinly sliced; 1 medium red bell pepper, cut into ½ pieces; 4 garlic cloves, finely grated; 1 1 piece ginger, peeled, finely grated; 1 tsp. garam masala; 1 tsp. ground coriander; 1 tsp. ground cumin; ½ tsp. ground turmeric; ½ tsp. mild chile powder (such as Kashmiri); ½ medium bunch cilantro, leaves and tender stems coarsely chopped, plus more for serving; ¼ medium red onion, chopped; 9 oz. sourdough bread, preferably day-old, cut or torn into 1 pieces (about 5 cups); 2 cups coarsely grated sharp cheddar (about 5 oz.), divided; Cilantro Chutney (optional; for serving)