Jefferson's Notes on Macaroni and the Macaroni Machine
In February 1789, William Short wrote to Jefferson that he had procured a "mould for making macaroni" at Jefferson's request in Naples, and had it forwarded on to his mentor in Paris. The macaroni mold probably did not reach Paris until after Jefferson had departed. His belongings were shipped to Philadelphia in 1790, and the machine was probably included with those items. We know that Jefferson did have the machine in the United States eventually, as it is listed in a packing list with other household items shipped from Philadelphia to Monticello in 1793.
Jefferson's notes on the macaroni machine read as follows:
"The best maccaroni in Italy is made with a particular sort of flour called Semola, in Naples: but in almost every shop a different sort of flour is commonly used; for, provided the flour be of a good quality, & not ground extremely fine, it will always do very well. a paste is made with flour, water & less yeast than is used for making bread. this paste is then put, by little at a time, vir. about 5. or 6. tb each time into a round iron box ABC. the under part of which is perforated with holes, through which the paste, when pressed by the screw DEF, comes out, and forms the Maccaroni g.g.g. which, when sufficiently long, are cut & spread to dry. the screw is turned by a lever inserted into the hole K, of which there are 4. or 6. it is evident that on turning the screw one way, the cylindrical part F. which fits the iron box or mortar perfectly well, must press upon the paste and must force it out of the holes. LIM is a strong wooden frame, properly fastened to the wall, floor, and ceiling of the room."
"N.O. is a figure on a larger scale of some of the holes in the iron plate, where all the black is solid, and the rest open. the real plate has a great many holes, and is screwed to the box or mortar : or rather there is a set of plates which may be changed at will, with holes of different shapes & sizes for the different sorts of Maccaroni." 
Jefferson was most likely not the first to introduce macaroni (with or without cheese) to America, nor did he invent the recipe. The most that could be said is that he probably helped to popularize it by serving it to dinner guests during his presidency. There is, however, a recipe for macaroni in Jefferson's own hand:
6 eggs. yolks & whites. 2 wine glasses of milk 2 lb of flour a little salt work them together without water, and very well. roll it then with a roller to a paper thickness cut it into small peices which roll again with the hand into long slips, & then cut them to a proper length. put them into warm water a quarter of an hour. drain them. dress them as maccaroni. but if they are intended for soups they are to be put in the soup & not into warm water
Primary Source References
1802. "Dined at the President's - ...Dinner not as elegant as when we dined before. [Among other dishes] a pie called macaroni, which appeared to be a rich crust filled with the strillions of onions, or shallots, which I took it to be, tasted very strong, and not agreeable. Mr. Lewis told me there were none in it; it was an Italian dish, and what appeared like onions was made of flour and butter, with a particularly strong liquor mixed with them."
1809 November 29. "Pd. John B. Sartori of Trenton 8. D. for 2. boxes Macaroni of 25. lbs. each.
1809 December 30. (Jefferson to Gordon, Trokes & Co.). "I have mentioned the article of Maccaroni, not knowing if they are to be had in Richmond. I have formerly been supplied from Sartori's works at Trenton, who makes them well, and would be glad to supply you should the Richmond demand make it worth your while to keep them. I paid him 16 cents the pound." [Letter goes on to order 20 lbs. of macaroni, among other items.]
1810 January 17. (Gordon, Trokes & Co. to Jefferson). "...the only Maccaroni in town is held by Mr LeForest which he says came directly from Italy, he asks 4/6 [per] lb which so much exceeds the price mentioned by you that we supposed it would be best to acquaint you of it before purchasing..."
1816 June 8. "Wrote to P. Gibson to remit John Steele Collector of Phila. 16.80 duties & portcharges on 50. bottles of Hermitage & a box of Maccaroni sent there by Stephen Cathalan of Marseilles."
↑PTJ, 14:540. See also continuing correspondence relating to the shipment of the macaroni machine in Volume 15.