Step 1 Preheat your oven to 180/Gas Mark 4.

Step 2 Cut a rectangle out of your sourdough to create a lid. Hollow out the rest of the bread and reserve the lid. 

Step 3 To make the white sauce: Half an onion. Wrap a bay leaf around it and stud with cloves to make an onion cloute. Infuse in the milk over a low heat.

Step 4 In a heavy bottomed saucepan, melt your butter over a medium heat and add in the flour to make a roux. It should be blonde in colour. 

Step 5 Add the milk gradually while stirring constantly. Once all the milk is incorporated, take the pan off the heat and add in 200g of grated Isle of Mull Cheddar and stir until it is fully melted. 

Step 6 In your sourdough, layer up the ham, sliced tomatoes and the rest of the cheese (sliced) and white sauce. Place the lid back on and brush the whole thing with 50g melted Hollis Mead butter. 

Step 7 Transfer to the oven for 20-25 minutes.