Special equipment: an 11-by-17-inch baking sheet
Put 1 1/2 cups warm water (about 110 degrees F) and 1 teaspoon of the sugar in a large bowl. Sprinkle the yeast over the top, and set aside until bubbly, 5 to 10 minutes.
Meanwhile, whisk together both flours and the salt in a medium bowl.
Once the yeast is ready, add the oil to the bowl, then the flour mixture. Stir together the mixture with a wooden spoon until a shaggy dough forms. Transfer it to a work surface dusted with all-purpose flour, and knead the dough until it is smooth, elastic and slightly tacky, about 5 minutes.
Lightly oil the bowl that held the flour mixture, put the ball of dough in it, cover and let rise in a warm place until doubled in size, about 1 hour.
Generously oil an 11-by-17-inch baking sheet. Punch the dough down, and transfer it to the baking sheet. Gently stretch and pat the dough to the edges of the baking sheet with your hands (it will recede slightly from the edges). (If the dough is resistant, let it rest for about 10 minutes, then try again.) Dimple the dough all over with your hands. Scatter the grapes over the top. Loosely cover, and let rise in a warm place until almost doubled in size, about 30 minutes.
Meanwhile, preheat the oven to 425 degrees F. When the dough is ready, uncover, generously drizzle with olive oil and sprinkle with the remaining 1 teaspoon sugar. Bake until the bread is golden brown and the grapes are soft and juicy, 20 to 25 minutes. Let cool in the pan on a cooling rack. Serve warm or at room temperature.
When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.) Never leave a child unattended in the kitchen. Limit the child to tasks that are safe and age-appropriate.
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