Line a loose-based, round tart tin with Borg's Shortcrust Pastry. Cover with baking paper and baking weights and blind bake at 180 C for about 15 minutes. Remove from oven, remove baking weights and cool.
Meanwhile, make the tart filling. Melt the butter over a medium heat and add the flour and mix together. Mix over heat for a few minutes until the flour has cooked out. Add the milk, and continue to stir over heat for about 8-10 minutes until the sauce has thickened and reduced.
Add in your flavourings, in this instance, KEEN'S Mustard Powder, salt, pepper and freshly ground nutmeg.
Add in the ham and stir to combine.
Remove from heat and cool, covered with baking paper. By putting cooled filling into your tart case, you reduce your chance of soggy pastry – that is why we do this step.
Spoon the cooled filling into the tart case and grate the gruyere cheese over the top.
Bake in 180 C oven for about 15 minutes until the cheese is bubbling and brown!
Remove from oven, let cool for a few minutes and then enjoy – this is the ultimate comfort food and so delicious!