Roast beef and potato salad rolls

For rolls, warm buttermilk and butter in a saucepan over low heat until butter just melts (2-3 minutes). Remove from heat, add 125ml water and stand until lukewarm. Meanwhile, combine remaining ingredients and 1½ tsp fine sea salt in an electric mixer fitted with a dough hook. Add buttermilk mixture and mix until a smooth sticky dough forms (5-7 minutes). Turn out onto a lightly floured surface and knead until very smooth, adding more flour as necessary to form a very soft dough (4-5 minutes). Transfer to an oiled bowl, cover with plastic wrap and refrigerate overnight to prove. Bring dough to room temperature (1-2 hours), then knock back and knead on a lightly floured surface until smooth. Divide into 10 balls, transfer to 2 large oven trays lined with baking paper, cover with a clean tea towel and set aside until doubled in size (30-40 minutes). Preheat oven to 180C, brush rolls with milk and bake, swapping trays once, until risen and golden brown (20-25 minutes). Rolls can be baked 8 hours ahead and stored in an airtight container.

For potato salad, boil potatoes in a saucepan of salted water until tender (25-30 minutes), drain and set aside to steam dry (30 minutes), then chop. Blanch beans until bright green (20-30 seconds), drain, refresh in iced water, drain and thinly slice. Combine remaining ingredients in a bowl, season to taste, add potatoes and beans, gently mix and refrigerate until required. Potato salad can be made a day ahead; add the herbs and green beans just before serving.

Preheat oven to 200C. Season beef with sea salt and black pepper, and drizzle with olive oil. Heat a large frying pan over high heat and sear beef for 1-2 minutes each side. Transfer to a roasting pan and roast until cooked to your liking (20-22 minutes for rare; internal temperature will read 60C on a meat thermometer). Transfer to a plate, cover with foil and rest for 20 minutes. Thinly slice beef and sandwich in rolls with potato salad.