Reduce heat to low and simmer for 8-10 minutes. Take off heat and set aside.
Add roasted sweet potato to a medium mixing bowl or high-speed blender. If using a mixing bowl, mash the sweet potato well before adding in the rest of the ingredients. If using a high-speed blender, place all of the sweet potato mash ingredients in at the same time, and blend until smooth.
Steam cauliflower until soft, about 5-7 minutes.
Place cauliflower and the rest of the cauliflower mash ingredients in a medium mixing bowl or high-speed blender. Mash or blend until smooth. Taste and adjust seasoning as desired.
Pre-heat oven to 350 °F.
Divide beef mixture between two similar sized cast iron skillets. Top one cast iron skillet with sweet potato mash and the other with the cauliflower mash.
Bake for 10 minutes and then broil on high for 5-8 minutes, or until the tops are golden.
*For the sweet potato mash: Roast sweet potato at 400°F on a lined baking tray for 45-50 minutes, or until fork tender. Once soft set aside to cool before making the sweet potato mash.
*Use ghee in the cauliflower mash to make it paleo-friendly!