(1) Preheat the oven to 400 F and line two baking sheets with parchment paper (2) Using a sharp knife or a mandolin, slice all of the vegetables into even, very thin rounds. Mix the oil, butter or ghee, orange zest and juice, thyme and salt in a large bowl. Add the parsnip and turnip and toss to coat. Transfer the rounds to the first baking sheet in a single layer (no overlapping). Repeat the process with the beet and sweet potato, placing them on the other sheet. (3) Bake the parsnip and turnip chips for 25 minutes, or until golden. Remove from the oven and transfer to wire racks to cool. You can store them in an airtight container for 2-3 days though they'll lose a bit of their crunch.