Preheat oven to 375 F and grease a 9x13 pan. Set aside.
Heat oil in a large saucepan and add the onion. Cook for 1-2 minutes or until the onions become translucent. Add ground beef and stir together and allow to brown.
In a large pot, add water until it’s ¾ filled and bring to a boil. Add pasta and let cook until al dente (not fully cooked – but almost). Approximately 7 minutes.
While the pasta is cooking, return to the ground beef and stir it until all the beef is browned. Add tomato paste, crushed tomatoes, sugar, pepper, salt, and parmesan cheese.
Once the pasta is finished cooking, run some cold water into the pasta water to make sure the pasta stops cooking. Once the water is mostly cold, strain pasta into a colander. Put the pasta back into the original pot and add butter and parmesan cheese. Stir thoroughly to incorporate.
To make the Bechamel sauce, add the milk to a medium saucepan and put on medium-high heat to heat the milk. Crack the eggs in to a separate bowl, whisk them thoroughly, and set aside.
In a separate small saucepan, make a roux with butter and flour. Wisk until fully incorporated and melted.
Continuing to stir the roux, add 3-4 ladles of the hot milk into the roux.
Add the roux mixture back into the milk saucepan and stir until combined. Add the pepper and nutmeg.
Once the milk mixture is boiling, take the whisked eggs and very slowly mix them into the milk and roux mixture – continuously stirring the mixture. Make sure to do this nice and slowly so that you don’t have scrambled eggs! Once the Bechamel is complete, remove from heat and set aside.
Take the 9x13 pan and assemble 1/2 of the pasta on the bottom of the pan. Take 2-3 ladles of Bechamel sauce and drizzle over the pasta, making sure each noodle is covered.
Add the fresh chopped parsley to the ground beef mixture and stir it in to make sure it’s fully incorporated. Layer all the ground beef on top of the pasta in the pan, making sure to evenly spread it. Add the remainder of the Bechamel on top and cover to the edges.
Sprinkle the cinnamon on top and put in the oven for 1 hour, or until the top is golden brown.
Once the Pastichio is out of the oven, allow the dish to cool 10-15 minutes and then serve.