Preheat oven to 200C, fan-forced. Line an oven tray with baking paper. Quarter the unpeeled potatoes. Quarter the carrot lengthwise. Strip the rosemary leaves, discarding the stems. Put the potato, carrot and rosemary on the lined tray, drizzle with 3 tsp olive oil and season with salt and pepper, then toss to coat. Roast for 25-30 mins until golden and tender.
Step 2 — Prep ingredients
Meanwhile, thinly slice the onion. Crush or finely chop the garlic. Crumble 1 stock cube* into a heatproof jug, add 180ml (¾ cup) boiling water and stir to dissolve.
Step 3 — Cook steaks
Heat a medium frypan over high heat until hot (it's important the pan is very hot before adding the steaks, otherwise they may stew slightly and become tough). Drizzle the steaks with 2 tsp olive oil and season with salt and pepper. Reduce heat to medium-high and cook steaks for 2-3 mins each side for medium-rare, or until cooked to your liking. Remove from the pan and rest for 3 mins.
Step 4 — Cook onion
While the steaks are resting, bring a small saucepan of water to the boil for the peas. Melt 10g butter in the frypan over medium-high heat. Cook the onion, stirring, for 3-4 mins until golden and softened.
Step 5 — Make onion gravy
Add the garlic and 1 tsp flour to the onion and cook, stirring, for 30 secs or until fragrant. Stir in the stock until combined, then bring to the boil. Cook for 2-3 mins until thickened. Stir in ½ tsp dijon mustard and season with pepper.
Step 6 — Cook peas and serve
Meanwhile, add the peas to the pan of boiling water. Return to the boil and cook for 1 min. Drain. Slice the steaks. Divide the steak, onion gravy, roast vegetables and peas among plates. Drizzle the steaks with any resting juices to serve.