For the garlic and lemon oil, place all the ingredients in a small saucepan over high heat. When the oil begins to bubble and fry the garlic and lemon, remove from heat and cool completely at room temperature, then strain. (Garlic and lemon oil can be stored in a clean airtight sterilised container in a cool place for up to a month.)
Heat 4 cups (1 litre) milk in a large non-stick saucepan over medium heat. Bring to a gentle simmer and, whisking continuously, pour in the semolina until combined and smooth. Simmer gently, stirring continuously, for 6-8 minutes until thickened. Stir in the cheeses and pepper. If the mixture is very thick, add a little more of the remaining 2 cups (500ml) milk. You want it to be porridge consistency. Season to taste. Remove from heat and stir in the butter.
Transfer to a large serving bowl and scatter with extra cheese and freshly ground black pepper. Drizzle with garlic and lemon oil to serve.
