Split Pea Soup

Ingredients

• 2 tbsp unsalted butter
• 1 large yellow onion, finely chopped
• 1/2 tsp salt
• 2 garlic cloves, minced
• 4 cups low-sodium chicken broth
• 3 cups water
• 1 pound ham steak, skin removed, cut into quarters (see note)
• 3 slices (4 ounces) thick-cut bacon, left whole (see note)
• 1 pound green split peas (about 2 cups), picked through and rinsed
• 3 sprigs fresh thyme, plus more for serving
• 2 bay leaves
• 2 medium carrots, cut into 1/2-inch pieces
• 1 medium celery rib, cut into 1/4-inch pieces
• Freshly ground black pepper
• Fresh croutons, for serving (optional; see instructions below)