Grease the inside of a 3-quart slow cooker with ½ tbsp butter.
In a medium skillet, melt the remaining ½ tbsp butter over medium heat.
Add the chopped onion and minced garlic.
Cook for about 5 minutes, stirring until tender.
Transfer to the slow cooker.
Add the sausages to the skillet and cook until browned.
Drain and add to the slow cooker.
Sprinkle half of the shredded Cheddar cheese over the sausage mixture.
In a large mixing bowl, whisk together the jalapeño (if using), eggs, salt, and pepper.
Stir in the chopped red bell pepper, then pour the mixture into the slow cooker.
Top with the remaining cheese.
Cover and cook on low for 7–8 hours, or until the eggs are fully set and the casserole is bubbly.
Serve warm.
Notes / Tips / Wine Advice:
Serving Tip:Serve with toast or a fresh fruit salad for a balanced breakfast.Wine Advice:Pairs well with a light sparkling wine or a citrusy mimosa for a brunch treat.