In a small saucepan over medium heat on the stove top or side burner, warm the olive oil. Once the oil is hot, add the onion and season with salt and pepper. Cook the onion until tender, about 5 minutes. Stir in the corn flour, cranberry juice, orange zest, orange juice, mustard, thyme leaves, port, and cranberries. Stir the sauce well and bring to the boil. Once the sauce is boiling, reduce the heat to low and simmer until thickened, about 10 minutes. Remove from the heat and set aside to cool.