Buttermilk: In a shallow dish, stir together the buttermilk and hot sauce. Add the beef liver pieces to the milk mixture, turning to coat. Cover with plastic wrap and chill in the fridge for at least 4 hours or overnight.
Bacon: Fry bacon in a large skillet over medium-high heat until crisp. Use a slotted spoon to remove from the skillet to paper towels to drain, then chop.
Add onion slices to the bacon drippings. Saute over medium-high heat for 3-4 minutes until softened and lightly browned. Remove from the skillet to a plate.
Make the Seasoned Flour: Use a whisk to combine the flour, seasoned salt, black pepper, granulated garlic, onion powder and paprika on a plate or in a shallow dish.
Remove the liver slices from the buttermilk brine, letting excess drip off. Coat on all sides with the seasoned flour.
Melt 2 Tbsp butter in the skillet. Fry the liver slices over medium heat for 3-4 minutes per side or until golden brown. (If cooking in batches, keep warm between batches and add additional butter, as needed)
Pile the onions on top of the liver slices. Cook for an additional 5 minutes or until the liver is tender (slightly pink in the middle) or 160°F on an instant read thermometer.
Serve immediately with the onions on top garnished with bacon and chives.
Optional Gravy Recipe: Remove liver from the skillet. Melt 2-3 Tbsp butter in the pan. Add 3 Tbsp all purpose flour to the melted butter. Cook over medium heat, scraping any browned bits from the bottom of the pan, cooking just until the flour has been absorbed. Gradually whisk in 2 cups of whole milk. Whisk until fully combined. Lower the heat to low and simmer for 5 minutes until thickened. Taste and adjust seasonings.Keep warm until serving drizzled over the liver and onions.