In a small sauté pan over medium heat, toast the fennel seeds for no more than 5 minutes, until fragrant.
Place all the ingredients except the butter in a large bowl and mix until well combined.
Divide the sausage mixture into 8 patties and flatten them between your hands.
In a large cast-iron skilletover low heat, melt the butter. Add 3 or 4 patties to the pan and cook for 5 to 6 minutes per side, until golden brown and cooked through. Keeping the heat on low will help cook the inside of the patties without burning the outside. Patience is key here.