Thinly slice your eggplants, place the eggplants on a wire rack and salt the eggplants. Let them sit for 20 minutes.
Pat them dry with paper towels.
For the Bechamel:
Add the mustard powder, nutmeg, and salt to the milk. Set aside.
Melt 1 tbsp. butter in a saucepan over medium heat and add the diced shallot. Sauce for 3 minutes. Now add the other 1 tbsp. butter and the 2 tbsp. of flour. Whisk constantly for 2 minutes until foamy. Add in the seasoned milk, and continue to whisk until the sauce thickens and coats the back of a spoon. This should be approximately 3-5 minutes.
Assembly:
Preheat the oven to 375 degrees.
Spread some béchamel onto the bottom of a baking dish
Place a sliced eggplant down on a cutting board. Spoon a layer of béchamel onto the eggplant. Next add a spoonful of sauce, then top with shredded mozzarella cheese. Roll the eggplant up and place it into the baking dish. Continue this process until all the eggplant has been used.
Bake for 35 minutes at 375 degrees. I like to broil the top for 3 minutes at the end to get a nice golden top. Garnish with fresh basil and enjoy!