Preheat the oven to 240C, or as high as it will go.
Toss the Brussel sprouts, sesame oil and soy sauce in a small baking dish and cover the tray tightly with foil. Place in the preheated oven for 10 minutes.
In the meantime, combine the peanut butter and vinegar in a saucepan and heat gently until softened and liquid.
Remove the sprouts from the oven, lift away the foil and pour over the softened peanut butter. Use a spatula to gently turn the sprouts over, so that every piece is covered in peanut butter. Return to the oven without the foil for another 10 minutes until the sprouts are completely soft and charred in places. Scatter over the cranberries and serve warm.