In a skillet over medium heat, warm olive oil. Add onion and cook, stirring frequently, until soft and translucent. Add garlic and season with salt and pepper. Remove from heat and stir in 2 tablespoons of butter, heavy cream, ham and swiss cheese. Add tortellini and stir until the cheese has melted. Transfer to the prepared baking dish and top with crushed crackers. Dot with remaining tablespoons of butter.