Preheat a 5-qt. cast iron Dutch oven over medium heat until the rim of the pan is hot to the touch.
Add the bacon and cook until slightly crisp.
Add the chopped leeks and sauté until tender, about 3 minutes. Reduced the heat to low.
Add the potatoes, stock, cream and jalapenos to the pan, cover and heat until just simmering. (Take care not to let the soup boil.) Simmer for 15 minutes or until the potatoes are tender.
Remove the pan from the heat and let it cool slightly.
Use a hand-held immersion blender (or process in batches in a standard blender) to puree the soup until smooth.
Return the soup to the pan and set the heat to low. Add the cheese and stir until completely melted and incorporated.
Season the soup to taste with salt and pepper and ladle into individual serving bowls.
Garnish each bowl with a slice of toasted baguette and a sprinkle of paprika. Serve piping hot.