Cost information for the following is not included. Normally this is because the quantity or ingredient is unknown
4 lrg fresh portobello mushrooms wiped clean,
  and stems removed
  Salt to taste
  Freshly-grnd black pepper to taste
4 lrg whole-wheat hamburger buns
  (or possibly large kaiser rolls)
2 x egg yolks
1 Tbsp. freshly-squeezed lemon juice