In a stand mixer, add the flour and dry yeast.
Run the mixer for a few minutes, then slowly start adding the water.
Add half of the water at first and after 5 minutes, gradually pour in the remaining water.
Once the dough starts coming together, add the salt and olive oil.
Increase the mixer speed and knead for 10 minutes.
Remove the dough from the mixer and fold it a few times by hand.
Place the dough in an oiled container, cover it with plastic wrap, and let it rise for 3 hours.
While the dough rises, cut the onions into medium-sized pieces.
In a large pot, heat some oil over medium heat and add the onions.
Season with salt, pepper, and fresh thyme.
After a few minutes of cooking, add the vinegar and sugar.
Cook the onions until they turn a caramel color, then let them cool.
Once the dough has risen, transfer it to an oiled baking sheet and spread it evenly.
Add the caramelized onions on top and let the dough rest for 30 more minutes.
Preheat your oven to 400°F (200°C) and bake the focaccia for 20 minutes.
Remove the focaccia from the oven, let it cool for a few minutes, and serve.
Enjoy your focaccia!