In a large, heavy stockpot, melt the butter over medium heat. Add the bacon and cook, stirring often, until the bacon begins to crisp, about 8 minutes. Using a slotted spoon, remove the bacon from the pan and set aside.

Reserve ¼ cup green onions. Add the remaining green onions, the celery, onion, jalapeño, and garlic and cook over medium heat, stirring often, until the onion is softened, about 5 minutes. Add the stock, potatoes, crisped bacon, 1 teaspoon of the salt, and the pepper. Simmer, stirring occasionally, until the potatoes are tender, about 15 minutes.

In a small bowl, whisk together the cornstarch and 2 tablespoons water to form a slurry. Stir the slurry into the broth and bring to a boil over high heat. Cook until slightly thickened, about 2 minutes. Reduce the heat to a gentle simmer and stir in the corn and cream, then return the chowder to a simmer. Add the salmon and season it with the remaining ½ teaspoon salt. Cover and simmer until the salmon is cooked through, about 10 minutes. Taste and adjust the salt as needed.

To serve, ladle the chowder into bowls. Top with the reserved green onions and additional black pepper. Add more jalapeños for extra heat.