For the focaccia:

1. In the bowl of a stand mixer, stir the yeast and water with a pinch of sugar. Let stand 5 minutes or until foamy.
2. Add the olive oil and whole wheat flour. Beat with a wooden spoon until blended and attach to the mixer with the dough hook.
3. Gradually add salt and bread flour, ½ cup at a time while mixing at medium low speed.
4. Knead for about 5 minutes and check to see if it needs more flour. It should be elastic and just a bit sticky.
5. If it's pooling too much in the bottom of the pan or too wet add more bread flour, by tablespoons, until you have a velvety dough that doesn't stick but is not stiff. I prefer to err on the wet side, since focaccia doesn't have to be formed into any shape and a too stiff dough will mean a tougher bread.
6. Coat a clean bowl with olive oil, transfer dough, turn to coat in the oil, cover and let rise until doubled at room temperature, about 1 to 1 ¼ hours.
7. Oil two 9x13x2 inch baking pans. Preheat oven to 400º.
8. Transfer dough to a barely floured board and divide in two.
9. Gather each half, place it inside the pans and, with oiled hands, press toward the borders until you fill the whole pan. If the dough resists, wait a few minutes and then stretch again with your fingers.
10. Liberally sprinkle with about ¼ cup olive oil each dough, scatter roasted grapes and rosemary on top, add sea salt to taste and let rise, loosely covered with plastic wrap, until almost double, 35 to 45 minutes.
11. Dimple the dough with your fingers one last time, and bake for about 20 minutes, until golden and top looks dry and crusty.
12. Let cool on wire rack for 5 minutes, transfer to wooden surface, add crumbled feta cheese on top, more olive oil and black pepper to taste.
13. Cut into squares and serve.

For Roasted Grapes:

1. Preheat oven to 350º.
2. Put seedless grapes on a baking sheet or oven pan, and sprinkle with only 1 teaspoon olive oil, rolling them around to coat.
3. Roast for about 20 to 30 minutes, until they just begin to collapse and brown.
4. Don't over roast them at this point because they will continue cooking with the focaccia.