Combine warm water, yeast, and sugar and let sit for 5-10 minutes—until the surface begins to foam.

Meanwhile, in a large mixing bowl, combine 2 cups of flour, salt and 1 tsp of rosemary.

Slowly pour water/yeast mixture into the flour mixture, stirring with a wooden spoon until well incorporated. Stir in extra flour as needed until dough begins to form—you may need up to a 1/4 cup.

Tip dough onto a well floured surface, and with floured hands, knead for five minutes. The dough will become smooth—not sticky. If it's still sticky, continue to sprinkle in flour while you knead, until a smooth dough is formed. Roll into a round ball and place in a lightly oiled bowl. Cover with a clean tea towel and place in a warm place to rise for at least 45 minutes. If I'm not rushed I like to let it rise for a good hour.

While the dough is rising, caramelize the onions. In a large stove top pan, over medium heat, add butter and olive oil. Stir in sliced onions. Let cook, stirring frequently for 20 minutes.

At the halfway point stir in sugar and salt.

Make sure to stir / scrape (with a wooden spoon) any brown spots that begin to appear. Add a few drops of water to help avoid sticking and burning.

After 20 to 25 minutes, your onions should be tender and golden. Set aside.

Uncover dough (it will have doubled in size) and tip onto a floured work surface. Knead for a minute or two.

Using a floured roller, roll into a large rectangle—approximately 6 x 20 inches. Transfer to a well oiled baking sheet.

Spread the caramelized onions evenly over half the dough, saving a tablespoon or two to garnish the top.

Fold the other half over the onions and pinch the dough edges together to seal.

Press into the dough (using your fingers) to create lovely little pockets all over the dough. Drizzle a tbsp of olive oil over the top, using a pastry brush to spread evenly.

Sprinkle the focaccia top with a pinch of kosher salt, and remaining rosemary / onions.

Bake at 425 for 25 minutes, or until the top is golden.