Plankstek (Nordic Steak with Baked Mashed Potatoes and Béarnaise)

Mashed potato plank

• 650 g Yukon Gold potato
• 120 ml Whole milk
• 70 g Unsalted butter
• 1 Egg yolk
• 1 ½ tsp Fine sea salt
• ½ tsp Black pepper

Béarnaise-style sauce

• 60 ml White wine vinegar
• 10 g Tarragon
• 2 Egg yolk
• 120 g Unsalted butter
• ¼ tsp Fine sea salt
• ¼ tsp Black pepper

Steak and mushrooms

• 2 pieces Beef sirloin steak, about 2.5 cm thick
• ¾ tsp Fine sea salt
• ½ tsp Black pepper
• 20 g Unsalted butter
• 250 g Cremini mushrooms

1. Heat the oven to 220°C (430°F). Peel the potatoes and cut into even chunks.
2. Put the potatoes in a saucepan, cover with cold water, and add 1 tsp of the salt. Bring to the boil, then simmer for 15 to 18 minutes until very tender.
3. Drain well, then return the potatoes to the hot pan for 1 minute to steam-dry. Warm the milk and 70 g of the butter together until the butter melts.
4. Mash the potatoes until smooth, then beat in the warm milk mixture. Beat in 1 egg yolk, then season with 0.5 tsp salt and 0.5 tsp pepper; the mash should be firm enough to pipe.
5. Spoon the mash into a piping bag (or a sturdy food bag with the corner snipped). Pipe a thick border and base onto a baking tray to form two planks with a shallow well in the centre.
6. Bake the potato planks for 18 to 22 minutes until lightly golden at the edges. Keep them warm while you cook the steak and mushrooms.
7. For the béarnaise-style sauce, put the vinegar and half the tarragon in a small saucepan and simmer until reduced by about half. Take off the heat and let it cool for 2 minutes.
8. Melt 120 g butter gently until just melted and warm, not sizzling. In a heatproof bowl, whisk 2 egg yolks with the warm vinegar reduction, then set the bowl over a pan of barely simmering water and whisk until thickened and pale.
9. Slowly whisk in the warm melted butter in a thin stream until glossy and spoonable. Stir in the remaining tarragon, then season with 0.25 tsp salt and 0.25 tsp pepper; keep warm off the heat.
10. Season the steaks all over with 0.75 tsp salt and 0.5 tsp pepper. Heat a frying pan over medium-high heat and add 20 g butter; when it foams, sear the steaks for 2 to 3 minutes per side until well browned.
11. Transfer the steaks to the oven for 4 to 8 minutes, depending on thickness and how you like them cooked, until done to your preference. Rest the steaks for 5 minutes.
12. While the steaks rest, slice the mushrooms and sauté them in the same pan over medium heat until browned and tender, 5 to 7 minutes. Taste and adjust seasoning if needed.
13. To serve, place each steak into the well of a potato plank and spoon the mushrooms alongside. Serve with the béarnaise-style sauce on top or on the side.

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