Cut the cauliflower into 5 thick slices, leaving the base intact.
Drizzle with olive oil and scatter salt over the top then massage the salt and oil in.
Place in the oven and roast for 35 minutes until tender and browned in places.
While that cooks, make the dressing.
Whisk together the olive oil, lemon juice, extra salt and mustard. Stir through the capers.
When the cauliflower is cooked and ready, remove from the oven and drizzle over the dressing. Serve with the extra dressing on the side.
Notes
I do not always leave the base of the cauliflower intact before I roast it. Basically it allows the veg to "hold together" and look like an actual steak, but it will taste just as delicious without the base intact.
Recipe by eatmystreet at https://www.eatmystreet.net/2017/07/26/cauliflower-steak-recipe-with-lemon-capers/