Stand mixer method:
Add warm water to the bowl of your stand mixer. Sprinkle yeast on top and wait until dissolved (30 seconds for instant yeast, a few minutes for active dry yeast). Add oil and salt.

Add roughly half of the flour and mix with the paddle attachment until all ingredients are incorporated (about a minute). Add the remaining flour and incorporate until all ingredients come together. Change to the dough hook and knead about 8 minutes. The dough is rather sticky but if possible do not add additional flour, which makes the focaccia less fluffy.

Generously oil a clean bowl with olive oil. Put the dough in and turn it around until coated in oil. Cover the bowl tightly (with a lid or cling wrap) and let it rise until doubled, for about 30 minutes at warm room temperature (in summer). It will take a little longer when colder.

Line a 9×13 inch (33x23cm) pan with parchment paper and additionally grease parchment with oil. Carefully transfer the risen dough to the pan and try to gently stretch it evenly without deflating the dough until it fills the baking pan.

Drizzle the dough with 1 tablespoon of olive oil and evenly distribute it on the surface with your fingers. Sprinkle thyme and rosemary over the dough, then dimple it with your fingers. Add tomatoes at this point. Do not add caramelized onions until later.

Let the dough rise a second time for 20-30 minutes until notably puffed. No need to cover during rising since the dough is oiled and won’t dry out. If you want to skip the second rise, see note. Add more oil before baking if needed.

Bake focaccia in the preheated oven at 400°F (200°C) until golden brown, about 15 to 20 minutes. If adding caramelized onion, add at 8 minutes before done. Cool baked focaccia bread for at least 10 minutes before slicing, better a little longer. If you are adding caramelized onions, top focaccia half way through baking. Any other topping can be put on in the beginning.