Preheat oven to 400°F. Cook bacon in a medium Dutch oven over medium-high, stirring occasionally, until crisp, 10 to 12 minutes. Transfer bacon to paper towels to drain using a slotted spoon. Pour drippings (you should have about ½ cup) from pot into a heatproof bowl; reserve. Do not wipe Dutch oven clean.

Return 2 tablespoons of the reserved drippings to Dutch oven over medium-high. Add onion. Cook, stirring occasionally, until slightly softened, about 3 minutes. Add garlic. Cook, stirring often, until onion is softened, about 2 minutes. Add stock, scraping bottom of pot to loosen browned bits. Add potatoes, pepper, and 1 ¼ teaspoons of the salt. Let mixture come to a boil. Reduce heat to medium-low; simmer, uncovered, 5 minutes. Stir in collards. Cook, partially covered, until potatoes are tender, about 15 minutes.

Meanwhile, arrange bread pieces in an even layer on a baking sheet lined with aluminum foil. Drizzle with 4 tablespoons of the reserved drippings; toss to coat. (Reserve any remaining drippings for another use.) Bake in preheated oven until crisp and golden brown, 10 to 12 minutes, stirring once after 7 minutes. Let stand at room temperature 15 minutes.

Spoon half of the collard mixture into a blender; process until smooth, about 1 minute. Pour into a large bowl. Repeat process with remaining collard mixture. Stir 1 ½ cups cream, hot sauce, and remaining ½ teaspoon salt into pureed collard mixture. Ladle soup into bowls. Drizzle with remaining cream, and top with croutons and bacon.