Preheat oven to 400 degrees F (200 degrees C). Lightly grease a 9x13-inch baking dish.
Cook and stir bacon, onion, and butter in a large skillet over medium heat until onions are translucent and bacon is cooked through but not crispy, 5 to 10 minutes; cool.
Place grated potatoes in a large bowl. Add bacon mixture, evaporated milk, eggs, farina, salt, and pepper to potatoes; stir to combine. Pour potato mixture into prepared baking dish.
Bake in the preheated oven for 15 minutes. Reduce heat to 350 degrees F (175 degrees C) and bake until top is golden brown, 1 hour.
