(If you are making Belgian fries with this http://www.recipezaar.com/288751 do everything including the first cooking of them before you start . it's all in the recipe above).
The first part is to fry up the mushrooms for later , we need em fried to add to the sauce , finely slice the mushrooms , the finer you slice em the more taste they give and the better your dish looks , i would suggest 8 slices per inch . Add about 2 teaspoons worth of butter in a hot pan , let your butter bubble out , when it's all quiet in the pan add the mushrooms and a small pich of salt. Your mushrooms will loose their moisture very quickly , so keep stirring them with a wooden spoon . when they are brown, reduced in size , and the moisture is gone , slide em in a bowl for later use.
Preheat your oven at the lowest setting 120-140°F (and put your plates in there).
Cooking the steaks . First of all , make sure there is fat on your meat . you don't necessarily have to eat it later , it is necessary for the cooking process . Frying a steak is done in a heavy cast iron frying pan , so if you have one , now is a good time to bring it out. Start by sprinkling some salt and pepper on both sides of the steak . Put 2 teaspoons of butter in your hot (quite high temp , max if cooker is electric) pan , let it quiet down , add in the steak ( it should chirp while putting it in there if it makes no sound your pan isn't hot enough ) well done = 3 minutes per side , 2 for saignant , 1 for bleux . while cooking move the meat around a bit , the fat on the meat should melt and make sure your meat doesn't burn. Put your steaks on a plate in the preheated oven so they can settle (your oven temperature should be low enough so they don't cook any more).
(now is the time to throw in the first batch of fries for the second cooking).
The sauce : Don't clean your pan after cooking ! you need the juices and the gristle in there for your flavor . Add the crème fraîche to your pan , put in the mushrooms you cooked earlier , add a pinch of salt and pepper and _keep stirring_ the sauce (on a high flame) until it is thick and creamy (take your time). Now add the teaspoon of port ( this is essential for the taste , as always when using alcohol in cooking , there is no actual alcohol in your dish , since it will have evaporated by the time you eat) .-your fries should be ready, take the basket out and shake em- Take the steaks out of the oven , put them on individual plates . If there is some juice on the plate you used in the oven , add that to the sauce , stir it in , divide the sauce on top of both steaks. Divide the garden cress onto the 2 plates(if you can't find garden cress , use finely sliced radish). Add Fries to the rest of the plate.
Have a nice meal !
(garden cress is very different from watercress , don't get confused , on wikipedia there are pictures of both).