Begin by gently husking the corn. Reserve the larger, outer leaves for wrapping the humitas. Slice the corn from the cobs with a sharp knife, and reserve the cobs. Grind the corn kernels in a food processor (or chop by hand) into pieces the size of a grain of rice; pour into a large mixing bowl, and set aside.
Melt the lard in a large skillet over medium heat. Stir in the onion and garlic; cook until the onion has softened, and turned clear. Stir in serrano peppers, green chiles, and red pepper; cook until softened. Stir the peppers into the corn, and season to taste with salt and pepper. Stir in the milk, then fold in basil, tomatoes, and Manchego cheese.
Bring a few inches of water to a boil in a large pot; fill a separate container with cold water. Dunk the corn husks into the boiling water for about 10 seconds to soften. Once soft and pliable, immediately dunk them into the cold water, then drain and set aside. Discard the boiling water.
Form the humitas by placing a few tablespoons of the mixture onto the bottom of a large husk (or two smaller husks overlapped). Form a packet by folding the bottom over once, then fold in the sides, and continue rolling into a packet. Tie with smaller strips of corn husk, or kitchen twine. Repeat until all of the filling is used.
To cook humitas, Place four corn cobs pointing top to bottom, into the bottom of a large Dutch oven. Arrange the remaining four cobs pointing left to right. This will form a platform for steaming the humitas. Pour about 2-inches of water into the pan, then arrange the humita packets on top of the corn cobs. Cover the pot, and bring water to a boil over high heat, then reduce heat to medium, and steam for 1 hour.