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 4-5 minutes or until the leeks are tender, stirring occasionally. Remove from heat.
To a food processor, add the leeks/garlic, nutritional yeast, vegan butter, almond milk, chives, thyme, salt, and black pepper. Lastly (once the cauliflower has let out all the steam) add to the food processor.
Starting on low speed, 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. Taste and add the remaining 1/4 cup almond milk if needed.
This recipe makes about 4 cups mashed cauliflower, or roughly 1 cup per serving. Add additional salt, black pepper, or nutritional yeast as desired. Store in an airtight container in the fridge for 2-3 days.
To freeze, cool the mashed cauliflower first and add to a freezer bag or airtight container, for up to 3 months. Add to the fridge overnight to thaw or reheat in a saucepan over low heat until thawed.