Blanch the potatoes in a saucepan of boiling water for 4–5 minutes until almost cooked. Drain into a colander. Layer the potatoes in a buttered 1.2 litre (2 pint) ovenproof dish with the onions, garlic if using, and seasoning. Pour the cream over the top and dot with butter. Cover and chill until required.
Make a slit down the side of each chicken breast and enlarge the slit to make a pocket. Divide the sun-dried tomatoes between the pockets, adding a sage leaf to each. Press a sage leaf on the top of each breast and sprinkle with seasoning.
Stretch the rashers of bacon by pressing a large cook's knife along the length of each. Wrap one rasher around each breast, then wrap a second at a different angle to the first to make a crisscross pattern. Put the breasts into a roasting tin with the ends of the bacon tucked underneath. Cover and chill until required.
When ready to serve, remove the covers and bake the chicken and potatoes in a preheated oven, 200°C (400°F), Gas Mark 6, for 30–35 minutes, alternating oven positions once during cooking until the potatoes and bacon are golden. Test the chicken by pressing a small knife into the centre of the breast; juices will run clear when ready. Transfer to serving plates and serve with a rocket salad, if liked.