Lunch

Rump Steak Sandwich with Balsamic Onions

Name: Rump Steak Sandwich with Balsamic Onions
Prep time: 25 min
Total time: 25 min
Yield: 1 serving
Ingredients: 150 g Rump steak, fat trimmed; 2 slices, about 100 g Sourdough; 100 g Onion; 1 tbsp (15 g) Balsamic vinegar; 1 tsp (5 g) Olive oil; 1 tsp (6 g) Dijon mustard; 20 g Rocket; To taste Salt; To taste Black pepper

Rump steak seared and sliced onto toasted sourdough with onions cooked slowly in balsamic, mustard and rocket. 43 g of protein for 540 kcal.

Calories: 540kcal
Protein: 43g
Fat: 13g
Carbs: 59g

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.
Sourdough2 slices, about 100 g
Onion100 g
Balsamic vinegar1 tbsp (15 g)
Olive oil1 tsp (5 g)
For the onions. The steak goes into a dry pan.
Dijon mustard1 tsp (6 g)
Rocket20 g
SaltTo taste
Black pepperTo taste

Method

Slice the onion thinly and cook it in the oil over a low heat for fifteen minutes, stirring now and then, until soft and golden. Add the balsamic and cook for two more minutes until it turns sticky.
Pat the steak dry, season it heavily and lay it in a very hot dry pan. Two minutes a side gives medium-rare on a steak 2 cm thick. Rest it on a board for five minutes.
Toast the sourdough. Spread one slice with mustard, pile on the rocket, then the steak sliced thinly across the grain with its resting juices, then the onions, and close.

Worth knowing

Resting is not decorative. Cut the steak straight from the pan and the juice ends up in the bread, which goes soggy, instead of in the meat.
Rump trimmed of its fat is 4 g of fat per 100 g. Sirloin is close. Ribeye is a different sandwich.

Other lunch recipes that share ingredients with this one, or every lunch between 450 and 600 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.