Sift the flour into a bowl, add the salt, egg and egg yolk, then gradually whisk in the milk to make a smooth batter. Set aside for 30 minutes.
Put the butter, sugar and syrup for the toffee sauce in a small saucepan and heat gently, stirring occasionally, until the butter has melted and the sugar dissolved. Bring to the boil and cook for 3–4 minutes until just beginning to darken around the edges.
Take the pan off the heat, then gradually pour in the cream. Tilt the pan to mix and as bubbles subside stir with a wooden spoon. Set aside.
Pour the oil for cooking the pancakes into an 18 cm (7 inch) frying pan, heat and then pour off the excess into a small bowl or jug. Pour a little pancake batter over the base of the pan, tilt the pan to coat the base evenly with batter, then cook for 2 minutes until the underside is golden. Loosen with a palette knife, turn over and cook the second side in the same way. When cooked, slide on to a plate and keep hot. Cook the remaining batter, oiling the pan as needed.
Fold the pancakes and arrange on serving plates. Top with banana slices and drizzle with the toffee sauce.