To prepare a yam and turnip stew with mini biscuits recipe, you'll first need to prepare the ingredients for the stew. Peel and slice the turnips and cut them in half lengthwise. Add the chopped onions, celery, thyme, and garlic to the saucepan and cook over medium-low heat until the onions are translucent and the garlic is fragrant, about 5 minutes. Remove the pan from the heat and add the mashed potatoes and stir to combine. Cook the potatoes until they are tender, 3 to 4 minutes, then stir in the butter and season with salt and pepper to taste. Simmer the vegetables for 10 to 15 minutes until all the liquid has been absorbed, stirring occasionally. Serve warm or at room temperature.