Add the sweet potatoes to a large saucepan, cover them with water add a generous amount of salt, bring to a boil and simmer on medium high heat with lid on for 7-8 minutes. Remove the cover and add cauliflower florets. Simmer for 10-12 minutes or until the vegetables are tender and not mushy.
Drain the vegetables well and place them back in the pot. Puree the vegetables in the food processor, do it in batches. Puree until everything is nice and smooth. Transfer to a big bowl and keep aside.
In a medium pan, add the butter and minced garlic. Cook and stir frequently over medium low heat till butter is melted. Cook till the butter is lightly browned. Stir in the thyme, salt, and pepper.
Pour the brown butter over the mashed vegetables and combine well. Taste and adjust seasoning. Enjoy