In a dry non stick pan toast the fennel seeds until fragrant, about 1 minute.
Place into a mortar and pestle and crush. Add the butter, herbs, garlic, lemon zest and seasoning mixing well.
Place a piece of baking paper on the bench, place the butter on it and mould into a log. Wrap, twisting the ends and refrigerate until needed.
Heat a barbecue or griddle pan to a high heat. Rub the steak with oil and cook for 3 or 4 minutes each side until done to your liking.
Serve with a slice of butter on top and roast chat potatoes