I use bakers percentage, which is an easy way of getting your dough mix right. The percentages are, for every 100g of bread flour (I use Shipton's English White) you need 65g (65%) room temperature water 40g (40%) of starter and 2g(2%) salt, I grind down sea salt which is not ionised.
For my Focaccia
1. Mix water and starter together in a bowl (large enough to take all ingredient) Mix with your hand, I always use my hand as I like to feel the dough
2. Add your flour, and again using your hand, grab the dough and twist your hand Turn the bowl through 90 degrees and repeat the grab and twist. Do this for about 3 mins. Cover the bowl and leave for 30mins. this gives the flour time to hydrate.
3. After 30 mins, sprinkle a little water on top of the mix then sprinkle the salt, the water stops the salt from drawing out moisture from your mix. Repeat step 2 grab and twist for 2 to 3 minutes. You can feel the salt grains, the mix will be easier to work because of the 30 min rest. Mix until the salt is amalgamated with the mix.
4. Cover, allow to proof either in a warm spot for about 4 hours, or overnight in the fridge.
5. Your dough should now show bubbles as the starter is activating the mix. Sprinkle a tablespoon of olive oil on the top of the dough. Put a little olive oil on your hand. Now it's time to stretch the dough, place your hand down the side of the bowl gently grab and pull the dough from the bottom of the bowl, twist the bowl through 90 degrees and repeat. Keep grabbing stretching and turning a few times.
6. The dough will need a baking tray with short sides, don't worry about that too much, just use what ever roasting pan you have. Mine is about 30cm (12 inches) by 45cm (18)inches. Spread a tablespoon of olive oil on the base of the tray, gently add your dough and allow to flatten and proof for another 4 hours covered.
7. Turn oven on to 220c degrees fan 240c none fan, gas mark 9. Your dough will have flattened a little and grown a little. Add about a tablespoon of olive oil to the top of the dough and sprinkle a little sea salt crystals. Oil your fingers and start to stretch the dough making multiple dimples and gently stretch. My mix filled my tray, it's not too thin or too thin, you should have bubbles over the dough and be around 15mm thick (1/2-3/4 inch). At this stage you can add other flavouring, I sliced very thinly a red onion and scattered over the dough. Experiment with yours.
8. When oven at temperature add your tray, check after 20 mins. There's no need to add steam to the oven. When golden brown, remove from the oven and allow to cool on a rack. While still warm, slice and enjoy. It can be served cool.