Retain 1/4 of the potatoes for the topping. Peel the rest of the potatoes, dice small and boil in a pan of water for 15-20mins until soft enough to mash. While the potatoes are boiling, prepare the onions below.
Place the sliced onions, grated apple, oil, xylitol, molasses and vinegar into a bowl, stir and leave to marinate while you prepare the rest of the recipe.
slice the retained 1/4 of the potato very thinly, use a mandoline for ease. Leave to one side.
Drain the boiled potatoes. Use a potato masher to mash until smooth then, add the flour, oil, herbs and salt. Use a spoon to combine the ingredients together until you form a ball of dough.
Place some greaseproof paper on to a level surface. Fold the potato mixture onto the paper. Use a spoon to flatten it slightly, ready for rolling. Dust with a little flour to prevent the rolling pin from sticking.
Use the rolling pin to ease the dough into a 20x30cm rectangle.
Lift the greaseproof paper (with the pizza crust o top) onto a baking tray. Switch the oven on to 180 degrees C.
Spoon the marinated onions onto the pizza crust. Do not allow too much of the juices to get onto the pizza crust as it will make it too soggy during cooking. The leftover juices can be spooned over the pizza after cooking or keep them for drizzling over a salad.
Layer the sliced potatoes on top of the onions. Brush with a little oil.
Slice the top off the bulbs of garlic, brush them with a little oil and place the bulbs NEXT TO the pizza. You can squeeze the garlic from the bulbs after roasting and it will spread like butter over the pizza.
You will only need to add the rosemary towards the end of cooking.
Place in the oven for 30-40 mins until the potato slices are crisping on the edges.
5 minutes before the end of cooking, scatter the fresh rosemary onto the pizza and return the tray back to the oven.
Once the pizza has cooked, take the tray from the oven, including the roasted garlic and leave it to cool for a few minutes.
After a few minutes, gently squeeze the garlic from the skin and add to the pizza.
Add a little of the juices leftover from the caramelised onions and serve.
Use leftover mashed potatoes from the day before to reduce prep time.