1. In a medium bowl, whisk together the milk, eggs, sugar and salt until combined. Pour the mixture into a shallow dish, then dip each slice of bread into the batter, stacking the slices and letting them sit in the dish while you heat the oil.
2. In a wok, heat the vegetable oil to 325° and line a sheet pan with a wire rack. Working with 2 slices at a time, shake off any excess batter and fry, flipping once until golden brown, 1 to 2 minutes per side. Transfer each slice to the prepared sheet pan to drain.
3. Divide the French toast between plates and top each piece with a heavy drizzle of sweetened condensed milk, then serve.