In a deep frying pan that will be able to hold liquid, melt the butter and stir in the onions. Fry until they become translucent, add 1 tbs olive oil and add the brats. Brown on each side, 5 minutes on each side, about 10-12 minutes total. when they have a nice color on each side, add the entire can of beer and let cook on medium high for half an hr to an hour.
For the salad dressing. In a bowl whisk together the 3 tbs olive oil, balsamic vinegar, agave nectar and Dijon mustard. Add a sprinkle of salt and some cracked pepper (I used 5 turns).To assemble the salads lay out 4 small bowls, add in spring greens, add 1 tbs Parmesan cheese to each bowl, 5-8 croutons per bowl and top with 1 tbs of the dressing.
To assemble the brats open bun and insert brat, and add some of the onions from the pot, spread with mustard or desired condiments.