Easy Steak Sandwich with Chimichurri and Sweet Balsamic Onions

My Auntie Mary has always been someone who knows what makes food good. Not fancy for the sake of it, not overcomplicated, just properly good. The kind of good that comes from knowing how flavours should work together, how something should feel to eat, and how one small detail can make all the difference. And when it comes to a steak sandwich, she has always had opinions.

She taught me early on that a good steak sandwich is not just about piling steak onto bread and hoping for the best. It has to be balanced. It needs freshness, richness, texture, and enough sauce or softness to bring it all together. It should feel generous and satisfying, but still easy to eat. No one wants a steak sandwich that looks great until the first bite, then turns into a tug-of-war with a piece of chewy steak hanging out of the bread.

That is probably why this version feels like the ultimate steak sandwich to me. It may not be the most traditional one, but it hits every note I want. It is fresh, filling, saucy, cheesy, and packed with flavour in a way that feels a little elevated without being hard to make. It is the kind of sandwich I would happily make for a weekend lunch, a casual dinner, or even cut in half and serve when people come over.

It starts with ciabatta, which I love for a steak sandwich because it is sturdy enough to hold everything together, but still soft enough once you bite into it. On the base goes mayonnaise or aioli, then rocket that has been dressed simply with olive oil and salt. That small step matters. Dressing the rocket makes it feel considered, not like an afterthought thrown in for colour. It gives the sandwich a peppery freshness that lifts all the richer elements and stops it from feeling too heavy.

Then comes the steak. I used rump here, cooked simply and sliced before layering it into the roll. One thing I think makes a huge difference is slicing the steak on the diagonal once it has rested. It gives you thinner, more tender pieces that sit better in the sandwich and make the whole thing easier to eat. You are not left pulling at big chunks of meat or losing half the filling on the first bite. Every layer feels more intentional that way, and every bite is better for it.

On top of the steak, I added Jarlsberg and melted it until soft and gooey. I love Jarlsberg here because it is mild, nutty, and melts beautifully without overpowering everything else. It gives you that proper steak sandwich comfort factor, but still lets the other flavours come through.

Instead of traditional caramelised onions, I made a quicker version with red onion, a little ghee or olive oil, and balsamic vinegar. Cooked down until soft and glossy, they become sweet, jammy, and full of flavour. They give you that richness you want from onions, but with a little tang and brightness from the balsamic that works so well with the steak.

And then the final thing that really makes this sandwich feel like mine is the chimichurri. Fresh parsley, coriander, olive oil, chilli flakes, salt, and a little vinegar, all blitzed together into a herby, punchy sauce. It cuts through the richness of the cheese and steak, adds freshness, and ties the whole sandwich together. For me, this is what takes it from just a good steak sandwich to the ultimate steak sandwich.

What I love most about this recipe is that it gives you the best of both worlds. It feels indulgent and comforting, but still fresh and vibrant. You get the richness from the steak and cheese, the sweetness from the balsamic onions, the peppery bite from the rocket, and the brightness from the chimichurri. Every layer actually has a job, which is probably exactly the kind of thing Auntie Mary would appreciate.

So no, this may not be the most classic steak sandwich out there, but it is absolutely the one I want to eat. The one I would make again. The one I would call ultimate. And sometimes that is what the best recipes are. Not the most traditional, but the ones built from everything you know and love about a dish, shaped into your own version of perfect.

The Ultimate Steak Sandwich

Serves: 2

Ingredients

• 2 ciabatta rolls

• 250–300g rump steak

• 1–2 tbsp mayonnaise or aioli

• 1 large handful rocket

• olive oil, for dressing rocket

• salt, to season

• 4 slices Jarlsberg cheese

For the balsamic onions

• 1 red onion, finely sliced

• 1 tsp ghee or 1 tbsp olive oil

• 1–2 tbsp balsamic vinegar

• pinch of salt

For the chimichurri

• 1 cup parsley, loosely packed

• 1/2 cup coriander, loosely packed

• 1 small garlic clove, optional but it makes sense here

• 1/4 cup olive oil

• 1–2 tbsp red wine vinegar

• pinch of chilli flakes

• salt, to taste

Method

1. Cook the onions
   Heat the ghee or olive oil in a pan over medium heat. Add the sliced red onion with a pinch of salt and cook until soft and jammy. Add the balsamic vinegar and cook for a few more minutes until slightly sticky and sweet. Set aside.

2. Make the chimichurri
   Add the parsley, coriander, olive oil, vinegar, chilli flakes and salt to a small blender or food processor. Blitz until combined but still a little textured. Taste and adjust seasoning.
   If it needs more brightness, add a touch more red wine vinegar.

3. Cook the steak
   Season the rump steak well with salt. Cook in a hot pan until done to your liking. Rest for 5–10 minutes, then slice thinly.

4. Dress the rocket
   Toss the rocket with a drizzle of olive oil and a pinch of salt.

5. Assemble
   Slice and lightly toast the ciabatta rolls if you like. Spread mayonnaise or aioli on the base. Add the dressed rocket, then layer over the sliced steak. Top with Jarlsberg cheese and melt it with a kitchen torch or under the grill.

6. Finish
   Spoon over the balsamic onions and top with the chimichurri. Add the lid and serve straight away.