In a dutch oven or large pan melt butter, add the onions and cook on low for about 30 minutes stirring occasionally until the onions are soft and start to appear golden. They should appear almost jammy when caramelized. Add the thyme and slowly add the apple cider a little at a time until cooked down and absorbed by the onions. Remove from heat and transfer into a bowl. Set aside until ready to serve.

Allow the steaks to come to room temperature before cooking. Heat a grill over medium-high heat. Season steaks with olive oil, salt and pepper. Sear on each side for 3-4 minutes for medium rare. Let rest under foil for 5 minutes. Cut into 1/2 inch strips.

To make the gravy: In the same pan as the onions, reheat 2 TBS of cider onions, when warmed add the steak drippings to the pan and allow to cook for 2 minutes. Slowly add the apple cider and worcestershire to the pan cooking until slightly reduced, 2-3 minutes. Remove from heat and add thyme, mustard and butter. vigorously whisk until combined and thickened. The gravy shouldn't be super thick but just enough that it will coat the steak nicely.

To serve: toast ciabatta, spread with mustard, generously layer cider onions, top with steak strips, spoon 1 tsp of the gravy overtop steak, finish with a handful of fresh rocket.

Serve immediately.