Preheat the oven to 350F and grease a 9” x 11” casserole dish. Slice 5 yellow squash into bite sized chunks, place on a paper towel, and sprinkle with salt. Allow this to rest for a few minutes until you notice beads of water being released.
Heat a large frying pan to medium-high heat and add 6 slices of bacon. Cook completely and remove the bacon to cool. Collect excess bacon grease in a bowl and set aside as we will add this to our creamy mixture. Allow the pan to remain hot and coated with a little bit of grease.
Slice ½ a yellow onion and add to the pan. Dab the yellow squash dry and add to the pan with onion after the onion has cooked for about 1 minute. Season with a pinch of salt and continue to cook until both the onions and squash are translucent and soft. Remove from the pan and place on a paper towel to drain. Set aside to cool.
In a separate large bowl, mix together ¼ sour cream, ½ cup mayonnaise, 1 egg, 2 tbsp bacon grease, ½ tsp salt, and ¾ tsp garlic powder. Add in 1 ¼ cup shredded cheddar and ½ cup shredded parmesan cheese.
Add the cooked squash and onion to the mixture until fully coated. Place the mixture into the greased casserole dish.
Crush 20 garlic butter Ritz crackers until they are fine crumbles and mix in with 3 tbsp melted butter. Top the casserole with the buttery cracker crumbles and bake in the oven for 40 minutes (give or take a few minutes depending on the thickness of your casserole). You will know it is done when it does not wiggle when you shake the casserole dish and the crust is golden brown.
Remove the casserole from the oven and allow to cool. Enjoy!