Preheat the oven to 400ºF.
Toss the tomatoes with 1 tablespoon of the olive oil in a small, heavy baking pan. Roast the tomatoes until blistered and tender, about 20 minutes.
Meanwhile, cut the bottom crusts off the bread and discard them. Cut the bread into ½-inch cubes. (You should have 4 loosely packed cups.) Stir together the remaining 2 tablespoons olive oil and the garlic in a large bowl. Add the bread cubes and toss to coat. Transfer the bread to a large rimmed baking sheet. Bake until golden and lightly crunchy, stirring occasionally, about 12 minutes. Reduce the oven temperature to 350°F.
Line 12 standard muffin cups with parchment liners or brush them with olive oil. In the large bowl used to toss the bread cubes, beat the eggs with the milk, cream, rosemary, and salt to blend. Season with pepper. Stir in 1 cup of the fontina and ¼ cup of the Parmesan cheese. Add the toasted bread cubes, stir to coat, and let stand 20 minutes.
Place a strip of prosciutto in the bottom of each muffin cup. Fill the cups about halfway with the bread mixture. Top the bread with more prosciutto and the roasted tomatoes, dividing the tomatoes evenly. Spoon the remaining bread mixture over the tomatoes and top with the remaining prosciutto. (Can be prepared 1 day ahead. Cover and refrigerate.)
Sprinkle the tops of the stratas with the remaining ½ cup fontina and ¼ cup Parmesan. Bake until the stratas are golden brown and set, about 25 minutes; cool slightly. (Can be prepared ahead: Enjoy warm or at room temperature within 4 hours, or refrigerate up to 2 days. If refrigerated, reheat on a pan in a preheated 375°F oven until warm, about 8 minutes.)
Excerpted with permission from <a href="https://www.amazon.com/gp/product/0847847470/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0847847470&linkCode=as2&tag=craftfocom-20&linkId=dbe1d47ede12a2437c868ce77de1cb71">The Portable Feast: Creative Meals for Work and Play</a> by Jeanne Kelley.