This can be made in the full quantity, half or a quarter. The image below is for the quarter quantity. You can add whatever you like as toppings.

The picture above has a little cheese, some parsley, onion rings and slices of olive as toppings.
Full quantity half quarter
400g Strong white bread flour 200g 100g
1 tsp Fast-action dried yeast 1/2 tsp ¼ tsp
4 tbsp Olive oil 3 tbsp 2tbsp
250ml Warm water 140 ml 80ml
1 tbsp Flaky sea salt 1½ tsp 1 tsp
Tip the flour, yeast, and 1 tsp salt into a large bowl stir to mix . Add 250ml warm water and 1tbsp of olive and mix with a wooden spoon to make a sticky dough. [half quantity is ¾ tsp salt and 1½ tbsp oil. 1/4 quantity is ½tsp salt and 1 tbsp oil] This dough should be quite wet so depending on your flour you may need to add a little more water.
Cover and leave to rise for 12 to 24 hours at room temp. If it’s particularly warm then you can also put it in the fridge overnight
The dough should double and be bubbly
Line a roasting tin with parchment – the tin size will vary depending on which quantity you use. Oil the parchment with a little of the olive oil and tip the dough in. Shape it to form a rectangle.
Scatter the remaining salt over and drizzle with 2 tbsp oil. Use your fingertips to create dimples in the dough, pressing in the toppings and spreading the dough to the corners.
If you wish to add toppings like rosemary or onion now is the time to add them.
Cover with cling film and leave to rise for 1 hr or until almost doubled in size. Heat oven to 220C/200C fan/gas 7 at least 20 mins before you cook the bread.
Uncover the dough, drizzle with the remaining oil and bake on the middle shelf for 30 mins until golden brown. Cool for 10 mins in the tin before transferring to a wire rack, or eat warm.