Preheat oven to 180c and prepare two baking trays lined with parchment paper.

To make the sauce, in a small saucepan, melt the butter over medium to low heat. Once melted, add the flour and whisk to combine. Cook for about 1-2 minutes until slightly golden in colour. Gradually add the milk and continue whisking to avoid lumps. Continue cooking and whisking until the sauce thickens, roughly about 5 minutes.

Stir in the Dijon mustard, salt, and pepper to taste. Remove from heat and mix in the ricotta and parmigiano reggiano cheese. Once combined, set aside.

To assemble, spread a layer of the cheesey béchamel sauce on the bottom of each of the croissants. Add the smoked ham along with a few slices of Mozzarella cheese. Place the top half of the croissant on top.

Add a thin layer of extra cheesey béchamel sauce to the top of each of the croissants and grate a little more parmigiano reggiano cheese over the top. Place into the oven and bake for 15-20 minutes, until the croissants are golden, and the cheese is melted.

Remove from the oven and grate more of the parmigiano reggiano over the top. Serve immediately.