Preheat the oven to 350 degrees F (175 degrees C).

Blend tofu, milk, salt, and pepper in a blender until smooth, adding more milk if necessary.

Combine spinach, Cheddar, Swiss, onion, and garlic in a medium bowl. Add tofu mixture and mix until well combined; pour into pie crust.

Bake in the preheated oven until set in the center and golden brown on top, about 30 minutes. Let stand for 5 minutes before cutting into six generous slices.