To begin, fill a large pot with water and bring to a boil over medium-high heat. Once boiling, add the cauliflower and boil for 10-15 minutes or until soft. Drain and leave the cooked cauliflower sitting in a colander in the sink to let any steam escape (note: this helps the puree to be smoother and not mushy).
Meanwhile, in a medium skillet, heat the unsalted vegetable broth (or olive oil if desired) over medium heat. Add the minced garlic and finely chopped leeks, and cook for about 3-4 minutes or until the leeks are tender, stirring occasionally. Add to a food processor.
Then to the food processor, add the nutritional yeast, vegan butter, almond milk, chives, thyme, salt, and pepper.
Once the cauliflower has let out all the steam, add to the food processor. Starting on low power, start blending and increase speed until creamy. You may need to stop the processor and stir in case some of the florets get stuck at the top. This recipe makes about 4 cups mashed cauliflower, or roughly 1 cup per serving. Taste and add salt, pepper, or additional nutritional yeast as desired. Store in an airtight container in the fridge for 2-3 days.