Combine flour, cornmeal, sugar, baking powder, thyme, and salt in a large bowl. Stir milk and hot sauce into the dry ingredients. Add the chopped onion, and mix thoroughly.
Using a cast iron skillet or other heavy bottomed skillet, heat 1 tablespoon oil over medium-high heat. Once oil is hot, drop the batter by rounded tablespoons into the hot skillet, flattening them slightly as you do. Fry until the fritters are golden brown on the bottom, about 2 minutes. Turn over, and fry on the other side until golden, about another 2 minutes. Remove the fritters to a paper towel lined plate. Oil the pan as needed to finish frying the fritters
Keep fritters warm in a low oven, about 200 degrees F while you fry the rest of the batter. Serve warm, plain or with sour cream for garnish.