Clean leek by cutting green area in quarters lengthwise. Rinse in water to get dirt and sand out. Then cut in quarters.
Slice mushrooms.
Put olive oil in pan and heat on medium high.
Add mushrooms and saute for 5 minutes.
Add leeks to mushrooms and continue sauteing until they form a crisp edge.
Add chicken stock and continuing cooking until reduces by half.
While chicken stock is reducing put pasta sheets into boiling water.
Twist the pot so the pasta sheets do not stick (sheets are done when you hold up a sheet and you touch the pasta and you can feel your fingers through the pasta).
After chicken stock reduces by half, turn fire down to low, add cream and mix thoroughly. Simmer 3 to 4 minutes.
Put pasta sheets on top of sauce and turn fire off.
Put chopped fresh tarragon on top.