Preheat water bath using immersion circulator to 129 degrees F.
Season steaks liberally with salt and pepper. Add to vacuum seal bag with sprigs of rosemary nestled along side each steak. Vacuum seal closed.
Add to water bath and cook for 1 1/2 - 3 hours.
While the steak is cooking, make the blue cheese gravy. In a medium sized saucepan, melt the butter over medium low heat.
Add the flour, whisk together, and cook for 2-3 minutes, whisking frequently.
Stir in the chicken stock and bring to a simmer. Simmer, whisking regularly, until mixture reaches desired consistency.
Remove from heat and stir in the salt, pepper, sour cream, and blue cheese. Taste and adjust seasonings to your liking.
When the steak is done cooking, remove from water bath and remove steaks from bag. Pat them thoroughly dry with paper towels.
Reseason the steaks with salt and pepper.
Preheat a cast iron skillet over high heat. Once very hot, add the ghee to the skillet. Sear steaks on each side for no more than a minute until well browned.
Top the steaks with plenty of blue cheese gravy and serve.