Stir together yeast, sugar and the warm water in the bowl of an electric mixer fitted with the paddle attachment. Let the wet mixture stand until foamy about 5 minutes.
Stir in 4 ½ teaspoons oil. Add flour and 4 ½ teaspoons salt, mix on medium-low speed until combined.
Place the dough hook in the mixer and knead the dough at medium speed until smooth, for 5 to 7 minutes.
Transfer the dough to a lightly oiled large bowl. Then cover loosely with plastic wrap and let the dough rise in a warm, draft-free spot until doubled in size, about 2 hours.
Preheat the oven to 180◦C. Generously oil a baking tray or place on a baking sheet. Spread out dough to fill sheet and working it in corners with your fingers. Press in tomatoes and sprinkle with rosemary. Then cover with oiled plastic wrap and let it rest for 30 minutes.
Pour the remaining olive oil over the dough and sprinkle with salt. Bake for 25 minutes at 180◦C (top and bottom air).
Let the focaccia cool and rest for about 20 minutes. If not serving that day, wrap the pieces in plastic wrap and foil. Freeze up to 1 month.
