Turn oven on warming setting. Pour about 1/4-inch of oil into a large cast iron skillet and heat over medium-high until hot but not smoking.
Thoroughly whisk the milk, eggs, sugar, and vanilla together and pour into a shallow bowl. Add 4 English muffin halves to the batter and soak, flipping frequently, until thoroughly saturated with liquid.
Add the muffin halves to the hot oil. Cook on the first side for about 30 seconds, flip and continue cooking until muffins are golden brown. (Reduce or increase heat, as necessary, to keep oil temperature hot but not smoking.) Gently shake excess oil from the muffins and place on paper towel lined sheet pan. Pat with additional paper towels to remove excess oil, if necessary. Hold cooked muffins in warm oven while continuing with remaining muffins.
Dust generously with powdered sugar and serve with warm maple syrup.