Render the pork fat: In a heavy pot, add the diced salt pork and cook over medium heat until the fat is rendered and the pieces begin to crisp. Add the sliced onion and cook for about 5 minutes, stirring often to prevent burning. Strain out and discard the pork solids, leaving the fat in the pot.
Parboil the potatoes: In a separate saucepan, place the sliced potatoes in boiling water and parboil for 5 minutes. Drain well.
Cook the chowder base: Add the drained potatoes to the pot with the rendered fat. Pour in 2 cups of boiling water and cook until the potatoes are tender, about 10 minutes.
Add the corn and milk: Stir in the corn and the scalded milk. Heat gently until the mixture reaches a simmer, but do not let it boil. Season to taste with salt and pepper.
Finish with butter and crackers: Stir in the butter. Soak the crackers briefly in a little cold milk until softened, then arrange them on top of the chowder. Serve hot, with extra crackers on the side if desired.
