Line a 9"x13" square pan with aluminum foil and lightly coat with cooking spray.

Combine buttermilk, cocoa powder, corn syrup, granulated sugar, salt and baking soda in a very large, deep saucepan/dutch oven. *Note: It's very important to use as deep of a pan as you have, 8 quart size or larger, in order to avoid the fudge boiling over.*

Heat fudge mixture over medium heat, whisking until there are no more lumps of cocoa powder.

When the mixture begins to boil, use a wet pastry brush to wash down any sugar crystals stuck on the sides of the pot, then clip on a candy thermometer and heat without stirring until the temperature hits 240 degrees F. *Note: It's very important to refrain from stirring at all while it cooks. If it starts to boil up high in the pan, threatening to boil over, still do not stir but instead turn the heat down a bit. It's fine if some ends up stuck to the side of the pot. You will still end up with enough in the end.*

When the temperature reaches 240 degrees F, pour out the fudge into the bowl of an electric stand mixer without scraping down the sides of the bowl. *Note: Simply let whatever pours out come out and dispose of the rest. Again, it's fine, you will end up with enough fudge. You don't want what is stuck to the side of the pot as it is going to be crystallized and will affect the consistency of the overall fudge in the end if it's included.*

Place the butter, vanilla extract and red food coloring in the bowl but DO NOT STIR. Clip the candy thermometer to the side of the bowl and go away for about 1+1/2 to 2 hours, until the temperature in the center gets down to 115 degrees F. *Note: It's very important to refrain from stirring. If you stir before the temperature gets low enough, the fudge will end up grainy instead of smooth like it's supposed to.*

When the fudge has cooled to 115 degrees F, mix using the paddle attachment on medium-low speed for about 10-12 minutes until the fudge thickens and is somewhat less shiny than when you began. *Note: If you don't have an electric stand mixer, you could use a handheld electric mixer. If you mix by hand it's going to take closer to 15-20 minutes and your arms are going to be seriously tired by the end. I highly recommend using an electric mixer, if possible.**Also Note: Don't worry too much about how shiny it is or isn't, as that doesn't seem to be a great indicator of when it's done. I mixed mine using my Kitchenaid stand mixer on level 3 for 12 minutes and it still seemed rather liquidy/gooey. I was pretty concerned but didn't want to over-mix it, so I just stopped it then. It came out wonderful after it set - firm enough to cut and had a velvet smooth texture. So my recommendation is to set your mixer on medium low and time it for 12 minutes, then stop and it should come out fine.

When the fudge is done mixing, pour into the prepared pan and allow it to set completely before frosting.

Beat together the butter, cream cheese and vanilla until smooth and creamy with no lumps.

Add in the powdered sugar and mix until creamy, fluffy and smooth. (you can mess with quantities a bit to get it the consistency you want. If it's too thick, add a tiny bit of milk at a time, mixing after each addition, to thin it out a bit. If you want it thicker, add in some more powdered sugar a small amount at a time, mixing after each addition until it reaches the desired consistency).

Spoon the frosting over the top of the set fudge and smooth out evenly across the top with a spatula.

Add red sprinkles, if desired.

Refrigerate the frosted fudge for about 1 hour to allow the frosting to set.

Once set, remove from the fridge and use the aluminum foil to lift the fudge out of the pan.

Peel the foil off the fudge and transfer the fudge to a cutting board, then cut into 1" pieces using a large knife. *Note: This fudge breaks apart fairly easily. I recommend running the knife under hot water and wiping it clean after every cut and pressing down on the knife evenly to avoid having the fudge crumble/break at the bottom.*

Store fudge in an air-tight container in the refrigerator for up to 2 weeks.

Fudge tastes best served at room temperature. Simply remove the desired amount of fudge about 1/2 hour prior to serving.