Open Beef Sammies with Caramelised Onions and Béarnaise Sauce

Steps

1. oven to 220°C. Line an oven tray with baking paper.
2. Toss roasties on prepared tray with a drizzle of oil and season with salt and pepper. Bake for about 25 minutes, until golden and tender. Turn once during cooking. While roasties are cooking, heat a drizzle of olive oil in a small pot on medium heat.
3. While oil is heating, slice onion very thinly. Cook onion, stirring often, for about 5 minutes, until soft and starting to colour. Add vinegar and sugar, stir, reduce heat to low-medium and simmer for about 10 minutes, until thick and glossy. Stir often to avoid burning.
4. Pat beef dry with paper towels and season with salt and pepper. Heat a drizzle of oil in a large fry-pan on medium-high heat. Cook beef for about 2 minutes each side for mediumrare (depending on thickness), or until cooked to your liking. Set aside, covered in foil, to rest for 5 minutes.
5. When roasties have 10 minutes cook time remaining, cut flattie into 2-3 pieces widthways, then carefully slice horizontally through the middle. Push roasties to one side of the tray and place flattie, cut-sides facing up, on other side of tray.
6. Return tray to oven to bake for final 8 minutes of cook time (for roasties), until flattie is lightly toasted. Thinly slice tomato and cucumber and add to a large bowl with mesclun, oil and vinegar. Toss to combine and season with salt and pepper. Slice beef thinly against the grain.
7. top a piece of rosemary flattie with caramelised onions, slices of beef and a good drizzle of béarnaise sauce. Divide open beef sammies, salad and roasties between plates.