In a jug, stir together all the Yorkshire pudding ingredients (flour, eggs, milk, salt) with a whisk until mostly smooth. Refrigerate until needed.
Make the sauce:
In a medium pot place the chopped tomatoes, garlic and mixed dried herbs. Heat on medium-low, stirring occasionally, until reduced by half. Stir in the balsamic and season with salt and black pepper, to taste. Set aside off the heat.
Bake the Yorkshire pudding:
Preheat the oven to 200C (400F). Place 1 tbsp of the rapeseed oil into an 8 or 9 inch oven-proof frying pan or skillet - you want one which is relatively deep. Place into the oven for 5-10 minutes so the oil gets nice and hot. Carefully pull the rack of the oven out and pour half of the Yorkshire pudding batter into the frying pan. Push the rack back in and close the oven door. Bake for 12-15 minutes until it's puffed up gloriously and golden all over.
Remove the hot frying pan from the oven (leave a tea towel on the handle so you don't end up grabbing scorching hot handle!!), spread a few tablespoons of the tomato sauce into the base of the pudding. Dot with half of the mozzarella and top with whatever toppings you'd like (I leave basil/rocket leaves to sprinkle on after it's baked). Sprinkle on some grated parmesan, salt and black pepper. Return the Yorkshire pud to the oven to bake for another 5-10 minutes until the cheese is melted and slightly browned. Slide the pudding out of the frying pan onto a cutting board and cut into slices using a large knife.
Repeat the baking and topping of the Yorkshire pudding to make 1 more pizza (using the remaining oil, batter and mozzarella) as before.