Heat a heavy pot over medium-high heat and cook the diced bacon until crisp, which should take about 5 minutes. Use a slotted spoon to remove the bacon and set it aside on a paper towel-lined plate to drain.

Remove all but 2 tablespoons of the rendered bacon fat from the pot. Add the butter and let it melt before stirring in the leeks and a small pinch of salt. Cook the leeks for about 5 minutes, stirring frequently, until they soften. Sprinkle in the smoked paprika and cook for an additional minute. Pour in the vermouth and simmer until the liquid is nearly evaporated, about 2 minutes. Add the stock, 1 cup of water, potatoes, thyme sprigs, and ¾ teaspoon of salt. Reduce the heat slightly and cook until the potatoes are tender, approximately 25 minutes.

Pour the milk into the pot along with the reserved bacon, and gently bring the chowder to a simmer. Add the fish chunks and cook for 2 to 4 minutes, just until the fish becomes opaque. Use a fork to break the fish into large flakes. Taste the chowder and adjust the seasoning as necessary. Remove and discard the thyme sprigs.

Serve the chowder hot, optionally garnished with parsley or scallions for added color and freshness.