Place the chicken cutlets on a clean work surface, narrow end facing you. Sprinkle with salt and pepper. Place one sage leaf crosswise on each of the pieces of chicken. Sprinkle each of the pieces of chicken with 1/2 ounce (about 2 tablespoons) of fontina cheese. Roll up the chicken and seal with one or two toothpicks. Warm the olive oil and halved garlic clove in a large, heavy skillet over medium-high heat until the garlic is fragrant, about 2 minutes. Add the chicken. Brown the chicken on all sides, about 3 minutes per side. Remove the chicken from the pan and remove and discard the garlic. Add the wine and simmer for 2 minutes while scraping up the brown bits from the bottom of the pan with a wooden spoon. Meanwhile, combine the tomatoes and red pepper flakes in a blender and blend until smooth. Add the tomato mixture to the reduced wine in the pan. Simmer for 5 minutes to let the flavors marry. Return the chicken to the pan. Simmer the chicken in the tomato sauce for 10 minutes. Turn the chicken over and simmer until cooked through, 5 to 7 minutes. Remove the chicken from the pan. Season the tomato sauce with salt and pepper. Spoon the tomato sauce onto serving plates or a serving platter. Slice the chicken into 1-inch rounds. Remove the toothpicks. Place the chicken over the sauce and serve immediately.