Cook and stir sweet potatoes, apples, ham, and leek in a large skillet over medium heat until tender, about 10 minutes. Allow to cool, about 20 minutes.
Mix cornmeal, flour, baking powder, and salt together in a bowl. Stir in cooled sweet potato mixture. Mix in milk and eggs until combined. Form mixture into 10 small cakes.
Heat 2 tablespoons oil in a large skillet over medium heat. Add 5 cakes; cook until browned and crispy, about 5 minutes per side. Repeat with remaining oil and cakes.
Heat chicken stock in a small saucepan over medium heat until warmed through, about 5 minutes. Stir in cornstarch slowly until stock is thickens slightly. Simmer until sauce is reduced, 3 to 5 minutes. Stir in maple syrup. Serve sauce with cakes.