Combine the corn, onion, garlic, and 1 cup of the stock; process in batches in a food processor until smooth.
In a big soup pot over med heat; melt the butter.
Add in corn mixture, cumin, salt, and white pepper.
Simmer, covered, for 5 minutes.
Add in buttermilk and 1 1/2 cups more stock; bring to a boil.
Add in chiles, Tabasco, chicken, tomato, and cilantro.
Lower heat to med-low; simmer, uncovered, for 30 minutes.
Add in remaining 1/2 cup stock if soup is too thick.
Serve in individual bowls topped with a few broken tortilla pieces; pass around the additional toppings.
Note: to crisp corn tortillas: preheat oven to 400°; brush or lightly spray both sides of tortillas with vegetable oil; stack 4 tortillas together; with a sharp knife, cut into 1/2-inch strips; place strips in a single layer on a baking sheet and bake for 3-4 minutes; sprinkle with salt or other seasonings; tortillas can also be fried in oil or grilled on a grill or griddle until crisp.