For the marinade: In a gallon re-sealable bag, combine all the ingredients and marinate for 1 hour at room temperature. Drain well and pat dry.
For the stew: In a large Dutch oven over medium heat, add the oil and the onions and cook until translucent. Remove from the pot and reserve.
In batches (if needed, do not crowd), add the steak to the pot and cook for 4 to 5 minutes per batch, turning to evenly and deeply brown. Adjust the heat as needed. Sprinkle with 2 tablespoons flour and stir to coat well.
Deglaze the pan with the whiskey and 1/2 cup of the beef stock, scraping any bits from the bottom. Add the remaining stock and return the onions to the pot. Add the bay leaves, thyme and savory and stir to combine. Bring to a simmer, reduce the heat to low, cover and cook for 2 hours, stirring occasionally.
After 2 hours have passed, add the potatoes, turnip and carrots. Cover and cook for an additional 35 to 45 minutes.
Add in the vinegar and salt, to taste.
In a measuring cup, combine the buttermilk and cream and whisk in the remaining 3 tablespoons flour. Add to the stew, stirring gently to combine, and cook for an additional 5 to 6 minutes. Turn off the heat, add in 2 tablespoons butter and serve.
Pair this hearty stew with a dry Irish stout.