Preheat the oven to 200C/400F/Gas 6.
For the garlic butter, place the garlic, olive oil, thyme, salt and freshly ground black pepper onto a small square of aluminium foil and fold up to make a parcel. Place into the oven and roast for 15 minutes, or until the garlic is soft.
Squeeze the garlic flesh from the skins into a bowl with the thyme leaves, softened butter, salt and freshly ground black pepper and mix until well combined.
Fry the pancetta in a frying pan until crisp, then add to the butter and mix well. Shape the butter mixture into a thick log and wrap in baking paper and cling film. Place into the freezer for ten minutes, or until firm. Once firm, cut into thick slices.
For the sirloin, rub the sirloin with the olive oil and season with salt and freshly ground black pepper. Heat a griddle pan until smoking, add the steak and fry for 3-4 minutes on each side (for rare), or until cooked to your liking. Remove the steak from the pan and leave to rest for five minutes on a warm plate.
For the kale, melt the butter in a saucepan, add the garlic and fry for one minute, then add the kale and fry for 2-3 minutes, or until wilted. Season with salt and freshly ground black pepper.
For the garnish, heat a dash of olive oil in a frying pan, season the tomato halves with salt and freshly ground black pepper and then fry for 2-3 minutes, or until just softened.
To serve, pile the kale onto a serving plate and top with the steak. Place a slice of garlic butter on top of the steak and spoon the cherry tomatoes onto the side of the plate.