SOAK THE WILD MUSHROOMS IN THE BOILING WATER FOR 20 MINUTES.REMOVE,SQUEEZE OUT EXCESS LIQUID,TRIM OFF HARD ENDS AND CHOP THE MUSHROOMS COARSELY. SAUTE THE MUSHROOMS IN THE BUTTER UNTIL LIGHTLY BROWNED.STRAIN ANY DEBRIS IN THE SOAKING LIQUID AND ADD TO THE PAN ALONG WITH THE SPINACH.COO UNTIL MOST OF THE LIQUID HAS BEEN ABSORBED.ADD THE HEAVY CREAM MIXED WITH EGG YOLK AND COOK GENTLY FOR 1 TO 2 MINUTES.SEASON TO TASTE WITH LEMON JUICE,SALT AND PEPPER.SERVES FOUR.