Place cubed sweet potatoes in a large pot and cover with 1 inch of cold salted water.
Bring to a boil over high heat, then reduce heat to a simmer for 5 minutes.
Add cauliflower florets to the pot and continue simmering for 10 to 12 minutes until both vegetables are fork-tender.
Drain the vegetables thoroughly in a colander and return them to the warm pot.
Place the pot over low heat for 60 seconds, stirring constantly to evaporate any remaining surface moisture.
Add minced garlic, butter, heavy cream, salt, and pepper to the vegetables.
Process the mixture using an immersion blender or food processor until smooth, or use a potato masher for a textured finish.
Garnish with chopped chives and serve warm.