In a bowl, combine the first five ingredients and mix with a wooden spoon to form a sponge. Cover with loose plastic wrap and let ferment for about an hour to an hour-and-a-half, until bubbles of differing sizes are on top.

Add ½ cup olive oil, the remaining 4 cups of flour and 2 teaspoons fine sea salt to sponge, mix well with a wooden spoon to combine. Turn out the mix onto a floured board, kneading for 5-7 minutes. Depending on the hydration of your starter, you may end up adding more flour while kneading, from ¼ to 1 cup. Use regular AP flour if adding any. The dough should be be soft and slightly moist.

Form into a ball and place in an oiled bowl or crock. Cover loosely with plastic wrap and allow to rise until doubled, about 1.5 to 2 hours.

Cover two baking pans (or a large one) with aluminum foil and oil them well, about ¼ cup of oil. Once dough has risen, place your dough in the prepared pan.

With your fingers, press dough into the bottom and sides of the pan until it fills the pan, but do not stretch too much. If your dough is very elastic and pulling away, allow it to rest for about five minutes and then continue.

Cover with a kitchen towel and allow to rise until roughly doubled in size, about an hour. A longer rise won't hurt the dough, either (I have left it to rise overnight at times).

Preheat oven to 400 degrees Fahrenheit.

Once dough is ready, lightly press the dough with your fingers all over, leaving little impressions. If the dough is a little dry on top, brush on a bit more extra virgin olive oil.

Now add your toppings. Be creative or traditional - rosemary, thinly sliced red onions, halved grape tomatoes (cut side up), or a mixture of herbs and salt all make good options.

Bake focaccia for 20 minutes or until golden brown. Then, if you have toppings, switch to grill setting and bake for an additional five minutes.

Remove from oven and cut into squares. Serve straight away, or allow to cool to room temperature and serve with some warm marinara sauce or whipped feta sauce.