To a large nonstick skillet set over medium-low heat, add the butter. Once melted, add the onions and sprinkle with brown sugar. Cook the onions for about 30 minutes, stirring occasionally until brown and caramelized. Transfer the onions to your slow cooker.
Also to the slow cooker, add the garlic, brown ale, beef broth, cream cheese, sour cream, mayo, worcestershire sauce, lemon juice, dried thyme, and cayenne pepper. Slow cook the dip on high for 1 hour and 30 minutes.
After 1 hour and 30 minutes, check the seasoning and add salt and black pepper as needed. At this point add the grated gruyere cheese, and slow cooker for an additional 30 minutes or until the cheese is melted.
Give the dip a good stir and then pour it into a serving dish. Serve the dip immediately with crostini and tortilla chips. Top with microgreens. Alternatively, this dip is also good served chilled. Transfer the dip to an airtight container and chill for at least 2 hours before serving. Enjoy!