Preheat the oven to 375°F (190°C).

Prepare the stuffing by heating a skillet over medium heat and sautéing the onion until translucent.

In a bowl, combine the sautéed onion, bread crumbs, cranberry sauce, chopped sage, egg, salt, and pepper.

Lay the flattened turkey breast on a clean surface and season it with salt and pepper.

Spread the stuffing mixture evenly over the turkey breast, leaving a small border around the edges.

Carefully roll the turkey breast away from you, tucking the stuffing tightly as you go.

Secure the roulade with kitchen twine or toothpicks at both ends and in several spots along the roll.

Place the roulade seam side down on a roasting pan and roast for 45-55 minutes, or until the internal temperature reaches 165°F (74°C).

Once cooked, remove from the oven and let the roulade rest for 10-15 minutes before slicing.

Slice and serve the turkey roulade with additional cranberry sauce, if desired.