Peel and thinly slice 6 potatoes (red or Yukon gold).

Heat enough olive oil in a deep 10-inch frying pan to cover the potato slices.

Add sliced potatoes, chopped garlic, and chopped onion to the hot oil. Cook uncovered until potatoes are tender but not browned.

While potatoes cook, whisk eggs and milk in a large bowl.

Drain most of the oil from the potatoes, reserving about 2 tablespoons. Add the hot potato mixture to the egg mixture and let rest for 10-15 minutes.

Season the potato-egg mixture with salt and black pepper.

Heat the reserved oil in a non-stick pan over low heat. Pour in the potato-egg mixture and cook until the bottom is set but the top is still slightly runny.

Place a large plate over the pan and quickly invert to flip the torta. Slide it back into the pan to cook the other side for 2-3 minutes.

Alternatively, after the bottom is set, transfer the pan to a preheated 400°F oven to finish cooking the top.

Let the torta rest for 15 minutes before slicing and serving warm or at room temperature.