I bought one for 71 cents and also picked up a Cheese Slider, which adds a piece of American cheese, for 89 cents.
The onions definitely make the slider. The patties were steamed on top of the onions, which were cooked until tender and wonderfully caramelized. It provided a strong accent to the beef as well as some sweetness.
The beef was very thin but moist from the steaming with a slight bit of onion notes from the cooking process.
The slider was surprisingly very airy and soft, perhaps almost overly so. It's satisfying in its own way but definitely different from your standard burger bun.
Overall, I enjoyed White Castle's Original Slider very much. The simplicity of it highlighted the essence of each component, which were each fairly well done. I'd definitely go with the cheese version over the original as the cheese complements everything nicely and provides an added textural element.
Nutritional Info - White Castle Original Slider (55g)
Calories - 140 (from Fat - 60)
Fat - 6g (Saturated Fat - 2.5g)
Sodium - 360mg
Carbs - 13g (Sugar - 1g)
Protein - 7g
Nutritional Info - White Castle Cheese Slider (63g)
Calories - 160 (from Fat - 80)
Fat - 9g (Saturated Fat - 4g)
Sodium - 500mg
Carbs - 14g (Sugar - 2g)
Protein - 8g