In a large bowl, mix flour, sugar, baking powder, baking soda, salt, and spices together until thoroughly combined. In a separate bowl, gently beat eggs, buttermilk, sour cream, and melted butter, until just combined. Add wet ingredients to dry, and mix gently. Batter should still be slightly lumpy. Do not over mix. Let batter sit for 10 minutes.
While the pancake batter rests, make your apple filling. In a medium skillet, melt butter. Add sliced apples, brown sugar and spices. Cook until apples are tender, 2-3 minutes. Stir frequently. Add cooked apples to pancake batter and gently stir to incorporate apples.
Melt butter in a non-stick griddle or skillet. Pour 1/2 cup of pancake batter onto griddle. Cook until edges are set and bubbles on the surface are just beginning to break, 2-3 minutes. Flip pancakes and cook until golden brown, another 1-2 minutes. Repeat with remaining batter.
While pancakes are cooking, make the syrup. In a small sauce pan, mix the apple cider and cornstarch together until the cornstarch is completely dissolved. Then add remaining ingredients. Bring to a boil and stir until syrup is slightly thickened. Keep warm until serving.
Serve warm pancakes with apple cider syrup. You could also add some toasted walnuts too.