Mac and cheese: cook 1 cup of macaroni per package instructions. This is typically something like: fill a pot 3/4 up with water and bring it to a boil. Add macaroni noodles and bring the water back to a boil. Once boiling, reduce the heat to keep the water simmering and cook for 8 to 10 minutes or until the noodles are tender.

Drain the pasta in a colander or strainer. While the pasta drains, return the empty pot to the stove and turn the heat under the pot to medium.

Add a tablespoon of butter and when the butter is melted and bubbling, add 1 tablespoon of flour. Stir until no dry flour is visible and cook the flour and butter for 1 more minute. 

Pour in 3/4 cup of milk and stir well. Bring the milk to a boil and reduce the heat until the liquid simmers. 

Once simmering, add garlic powder, salt, and ground black pepper. 

Add cheese, a handful at a time, and stir until that cheese is melty before adding another handful. Continue until all of the cheese is melty and the sauce is smooth. 

Pour the drained macaroni noodles back into the pot with the cheese sauce and stir until all noodles are coated with cheese. 

Add all of the mac and cheese into an 8 x 8-inch baking dish and with a spoon or spatula spread it out until it's in an even layer. Cover the dish with a lid or plastic wrap and place in the fridge for 1 hour or overnight to solidify. 

Peas cheese slices: add a greased or Silpat lined sheet pan to your oven on its lowest setting. Mine is 150 F (65 C). 

Drain 3 tablespoons of canned peas and give them a rough chop just to break up some of the peas. 

Add water to a medium-sized pot and bring to a simmer. Add sodium citrate and stir to combine.

Slowly add all the shredded cheese, stopping to stir the cheese into the sauce after every handful. Once all the cheese is added stir very well while the cheese is still simmering to make sure it is very smooth. Add the peas and stir until they are fully incorporated in the sauce.

Once the peas and cheese mixture is very smooth, carefully pour the sauce over the warm sheet pan and shake the sheet pan to allow the sauce to spread out. You may need a knife or offset spatula for this. 

Cover the cheese with parchment or wax paper, press down with your hands to flatten the cheese sauce, and move the pan to a refrigerator to cool for around at least an hour.

Once the peas cheese is fully cool, you can carefully remove it from the sheet pan and slice the cheese into 3.5-inch squares or whatever shapes you desire. To store the cheese, place a piece of parchment or wax paper between each slice and store it in the refrigerator for up to three weeks. 

Warming the ham: in a skillet over medium heat, warm the slices of ham. This should only take about 5 minutes or you can cook longer if you prefer to brown the ham.

Sandwich assembly: once the ham is warmed, add a slice of Peas Cheese to a slice of bread and top with the ham slices. 

Cut out a bread slice-sized rectangle of cold mac and cheese and carefully spatula it on top of the ham slices. Cover the mac and cheese with the second slice of Peas Cheese and the second slice of bread. 

Sandwich grilling: wipe out the pan that you used to warm the ham place it back over medium-low heat and allow the pan to warm up for 5 minutes. 

Spread a teaspoon of butter on the outside of one piece of bread and place it butter-side down in the warm pan. Cook for 3 minutes and check to see if the underside of the bread is starting to get toasty. Keep checking every minute or so until it starts to look golden brown. When it does, spread the second teaspoon of butter on the top exposed slice of bread and flip the sandwich.

Cook the second side for about the same amount of time as the first side, checking every minute or so for browning. If the cheese looks like it's not getting melty at all when you flip the sandwich, cover the pan with a pan lid or sheet pan while you cook the second side. This will help to steam the interior of the sandwich to melt the cheese.

When both sides of the sandwich are golden brown, move the sandwich to a cooling rack and remove the pan from the heat.

Serve and enjoy.