In a deep skillet, saute butter and onion for about 5-7 minutes.
Add chicken breasts to pan, and top with the seasonings while the bottom side is browning. Once brown, flip and repeat seasoning on opposite side.
Once both sides are browned, add one can of beer to start (about 1/3 or 1/2 way up the sides of chicken breasts). Cover and simmer on low for about 1 hour (when the beer is almost evaporated). Once the liquid is almost evaporated, add the second can of beer. Cover, and simmer for an additional hour.
You can let it cook longer if needed, just make sure there's always liquid in the bottom of the pan.