Preheat the oven to 180 C / Gas 4. Line a baking tray with some baking parchment to help with the washing up.
First of all, make a silky cheese sauce. Melt the butter in a saucepan in a medium heat and then stir in the flour to make a roux. Gently cook until the roux is sizzling, then pour in the milk whisking all the while. Use your wooden spoon to collect all the roux from the corners of the pan, still whisking frantically.
Cook until the sauce is gently bubbling, still stirring and whisking and then bubble for a few minutes until the taste of the flour disappears. Add the cheese, bar around 25g, stirring it in well, and then season generously, especially with black pepper. It forms a great partnership with the cheese. Remove the sauce from the heat and set aside.
Cut four holes, around 5cm in diameter, in to the top of the baguette. Remove the crust and then hollow out a little of the soft bread. Make sure that you don't cut straight down through the crust below. Line the hole with the ham slices.
Break open the eggs and let around half of the white fall away. Perhaps keep that for making macaroons or meringues! Then carefully slide the yolk into the bread cavity along with ham. Spoon the sauce over the top, being as generous as you dare!
Bake the baguette for 12 minutes until bubbling. Remove from the oven cut into four portions, either side of the egg and serve with a chilled pastis or biere blond.