Add the water, yeast and sugar in the bowl of a stand mixer or regular bowl, cover and let sit for about 10 minutes until the mixture starts to get bubbly.

In a separate bowl add the flours and sea salt and whisk to combine. 

Fitted with a dough hook, start the stand mixer and slowly, add in the flour. Knead until a dough forms.  Turn out onto a lightly floured surface and clean out the bowl, then grease it with a tablespoon of olive oil. 

Place the dough back into the bowl and coat with the oil, cover tightly and let rest for about 2 hours. 

After the dough has doubled in size, grease a cast iron skillet or 9 x 13 inch sheet tray with 1-2 tablespoons of olive oil and tilt the dough onto the skillet or tray and pat it evenly across the surface. Cover again and let rest for another 1-2 hours. 

About ½ hour before you bake the focaccia, place a rack in the middle of the oven and preheat it to 425°F (210°C). Pour two tablespoons of oil over the dough.  Rub the oil evenly over the dough and, using all of your fingers, press down to create deep dimples. If necessary, stretch the dough as you dimple to allow the dough to fill the pan. Decorate with rosemary sprigs and cherry tomatoes to create a Christmas tree. Sprinkle with flaky sea salt all over.

Transfer the pan to the oven and bake for 25 to 30 minutes, until the underside is golden and crisp. Remove the pans or pan from the oven and transfer the focaccia to a cooling rack. Let it cool for 10 minutes before cutting and serving.