1 Remove the sausage from its casing: Using a very sharp knife, make a slit in the casings by running the tip of the blade down the length of the sausage.
Remove the casing from each of the bratwurst and discard.
2 Cook the sausages: In a cast iron skillet, or other heavy nonstick skillet, brown the brats over medium high heat and cook for 5 to 6 minutes, until the meat is cooked through and developing some caramelized spots. Break up the sausages with a wooden spoon or a potato masher as you cook—aim for bite-sized pieces the size of raisins, which are perfect for scooping with chips.
Use a slotted spoon to transfer the browned sausage to your slow cooker. Leave the fat behind in the pan; you will use it for the next step.
3 Cook the onions and garlic: Add the onions and garlic to the hot pan and for 3 to 4 minutes, or until the vegetables look translucent and glossy.
4 Add the beer: Lower the heat to medium-low, and carefully pour the beer into the pan. The beer will steam and fizz, so be careful. Using a wooden spoon, scrape up any browned bits of food that are stuck to the bottom of the pan. This deglazing of the pan is important as it adds tons of flavor to the finished dip.
Bring the liquid to a boil and let it bubble for about 2 to 3 minutes, until slightly reduced. (This also cooks off the alcohol.)
5 Prepare and add the thickener: While the beer is cooking, whisk together the cornstarch, whole milk, Dijon mustard, salt, white pepper, cayenne pepper, and the ground nutmeg in a mixing bowl to form a smooth mixture.
Once the beer has reduced, carefully pour the cornstarch mixture into the skillet, whisking constantly. Increase the heat to medium and bring the mixture back to a boil. It should thicken quickly.
Once the mixture has the consistency of gravy and the whisk leaves a ribbon when pulled through the sauce, remove the pan from the stove and carefully pour the sauce into the slow cooker.
6 Add the cheese to the slow cooker: Stir the cheese, one type at a time, with the other ingredients in the slow cooker. Make sure to stir thoroughly before adding the next one.
Stir in the drained, diced pimentos.
7 Cook the dip: Cover the slow cooker and cook the dip on high for 30 minutes to melt the cheese.
8 Hold the dip on the “warm” setting and serve: Once the cheese has melted completely, switch to the warm setting and stir the dip. Add the chopped cilantro and stir once more. Adjust the seasoning to suit your taste by adding more salt and/or pepper. I’ve found that the flavors deepen as the dip sits and it may seem to get saltier, so I recommend erring on the side of under-seasoning at this point.
This dip will keep (on warm) for up to four hours. Give the dip a stir every half hour or so to prevent a skin from forming on the top. If you feel like it’s getting to thick, stir in a little milk to thin it out again.
9 To serve: Spoon the dip onto individual plates, or into bowls. Enjoy with tortilla chips or good ol’ Bavarian-style pretzels!
Leftovers can be stored in a food storage container in the refrigerator for up to two days.
To reheat: Heat on high for one minute in the microwave. Stir the dip and reheat at 30-second intervals, stirring after each interval, until warmed through.