Bake for 10-15 minutes until golden brown and soft.Set the garlic aside to cool.Place the cooled garlic, egg, mustard, salt and pepper in a food processor and blend on medium for 3 minutes until well blended.Add the oil to a measuring jug and very slowly pour it into the blending food processor until it is all combined.Add the optional lemon juice if the mixture become too thick.Place in an airtight jar and store in the fridge for up to 3 weeks.