In a large mixing bowl, add the sugar and lemon zest. Using your fingertips, rub the lemon zest into the sugar to release the oil.
Crack the eggs into the mixing bowl and whisk for 2-3 minutes or until they're foamy and have lightened in colour.
Add the milk, melted butter and vegetable oil. Whisk again to combine fully.
Sift the flour, baking powder and a smallish pinch of salt over the other ingredients and gently fold to incorporate until no lumps of flour remain. Be gentle when folding and try not to over mix.
Cover and chill the cake batter for at least one hour. When ready to bake the magdalenas, preheat the oven to 220ºC / 200ºC Fan / 425ºF / Gas Mark 7. Line a 12-hole muffin tin with paper liners. Evenly distribute the cake batter between the paper liners. Sprinkle the tops with a little extra sugar.
Bake the muffins for 10 minutes, then turn the oven temperature down to 200ºC / 180ºC Fan / 400ºF / Gas Mark 6 and continue baking the muffins for a further 5 minutes until the muffins are well risen and a skewer, when inserted in the centre, comes out clean without any uncooked batter remaining.
Leave the muffins to cool for a few minutes in the muffin tin, then transport them to a wire rack to finish cooling completely. These muffins are best eaten fresh on the day of baking, but they will keep for up to 3 days stored at room temperature.