Heat a large soup pot or Dutch oven to medium heat. Add pancetta; cook until browned and crisp, 4-5 minutes. Remove to a paper towel-lined plate; set aside.
Add 2 tablespoons butter, onion, carrot and celery to the pot. Cook, stirring often, until softened and lightly browned, 9-10 minutes. Add garlic; cook until fragrant, 30-60 seconds. Transfer vegetable mixture to a bowl; set aside.
Add remaining 3 tablespoons butter to the pot. Stir in sweet potatoes; cook until slightly soft, 7-8 minutes, stirring occasionally. Stir in chicken broth, salt, sage, thyme, smoked paprika, crushed red pepper flakes, pepper, cooked vegetable mixture and 2 tablespoons cooked pancetta. Bring to a boil; reduce to a simmer. Cook until potatoes are tender, 5-7 minutes, stirring occasionally.
Whisk about 1/4 cup of the hot broth into the half-and-half to temper; slowly add half-and-half mixture to the soup, stirring constantly. Stir in kale; simmer until wilted, 4-5 minutes. Remove from the heat.
Ladle soup into bowls. Top each with remaining cooked pancetta, pepitas and sage, if desired. Serve immediately.