Dinner

Open Steak Sandwich with Caramelised Onion

Name: Open Steak Sandwich with Caramelised Onion
Prep time: 25 min
Total time: 25 min
Yield: 1 serving
Ingredients: 150 g Rump steak, fat trimmed; 1 slice, about 50 g Sourdough; 120 g Onion; 5 g Olive oil; 2 tsp (10 g) Balsamic vinegar; 1 tsp, about 6 g Dijon mustard; 30 g Rocket; To taste Salt

Sliced rump on one slice of sourdough with slow-cooked onion, mustard and rocket. 39 g of protein for 426 kcal.

Calories: 426kcal
Protein: 39g
Fat: 12g
Carbs: 36g

Per serving, makes 1. 25 minutes of work. Published 8 September 2026.

Allergens

Gluten
Mustard
Sulphites

Nearly every bottle of balsamic lists sulphites.

Flags follow UK labelling rules and come from the ingredients as listed, not from any particular brand. Check the packet before cooking for somebody with an allergy.

Ingredients

Rump steak, fat trimmed150 g
Weighed raw. The same piece weighed after cooking has lost water, so the protein per gram is higher and the total would come out about a quarter over.
Sourdough1 slice, about 50 g
Onion120 g
Sliced thin. It cooks down to a third of its size.
Olive oil5 g
Balsamic vinegar2 tsp (10 g)
Dijon mustard1 tsp, about 6 g
Rocket30 g
SaltTo taste

Method

Cook the onion in the oil over a low heat with a pinch of salt for twenty minutes, stirring now and then, until soft and brown. Add the balsamic for the last minute.
Sear the salted steak in a separate hot pan for three minutes a side and rest it for five.
Toast the sourdough. Spread it with the mustard, pile on the onions, then the sliced steak and its juices, then the rocket.

Worth knowing

One slice of bread rather than two takes 120 kcal off and the sandwich does not miss it. Eaten with a knife and fork.
The onions take twenty minutes and cannot be hurried. A high heat burns the edges before the middle softens.

Other dinner recipes that share ingredients with this one, or every dinner between 300 and 450 calories a serving.

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Macros are calculated from the weights listed above using standard food composition values, and will shift with your own brands and measuring. Weigh what you can. This is a recipe, not dietary advice. The full health disclaimer is below.