Pressure cooker: Heat the butter using the saute function (in the InstantPot) or by heating the pressure cooker over medium heat on the stove (for stovetop pressure cookers). Add the onion, garlic and carrots, and saute for 2-3 minutes, until onions are translucent.Add the tomatoes, pumpkin, squash, chicken broth, sugar, salt, parsley, pepper, Italian seasoning, and cayenne. Stir to combine. Close the pressure cooker and bring to high pressure. Cook for 20 minutes. Let the pressure cooker naturally release for 10 minutes, then release the rest of the pressure.Use an immersion blender (or transfer the mixture in batches to a blender - taking care as hot liquids expand while blending) to blend until smooth. Stir in the half and half or cream. Thin with additional broth or cream/milk, if needed. Serve over hot, cooked pasta and garnish with Parmesan cheese.For the slow cooker: Combine all the ingredients in a slow cooker and cook on low for 4-6 hours until the squash is tender and flavors have combined well. Use an immersion blender (or transfer the mixture in batches to a blender - taking care as hot liquids expand while blending) to blend until smooth. Stir in the half and half or cream. Thin with additional broth or cream/milk, if needed. Serve over hot, cooked pasta and garnish with Parmesan cheese.For the stovetop: Heat the butter in a 4- or 5-quart pot (or similar size) over medium heat. Add the onion, garlic and carrots, and saute for 2-3 minutes, until onions are translucent.Add the tomatoes, pumpkin, squash, chicken broth, sugar, salt, parsley, pepper, Italian seasoning, and cayenne. Stir to combine. Bring the mixture to a gentle simmer and cook, covered, for 50-60 minutes until the squash is tender, stirring every once in a while to make sure the sauce doesn't stick (reduce the heat as needed). If it looks like it's reducing while cooking, add another 1/2 cup of broth or so.Use an immersion blender (or transfer the mixture in batches to a blender - taking care as hot liquids expand while blending) to blend until smooth. Stir in the half and half or cream. Thin with additional broth or cream/milk, if needed. Serve over hot, cooked pasta and garnish with Parmesan cheese.