Lace cookies/lemon-buttercream filling

---------- Recipe via Meal-Master (tm) v8.05
  
       Title: Lace Cookies/lemon-Buttercream Filling
  Categories: Cookies
       Yield: 30 servings
  
            Filling:
       2 ts Cornstarch
       2 tb Fresh lemon juice
       4    Egg yolks; room temp
     1/4 c  Sugar
      10 tb Unsalted butter; * see note
       1 ts Finely grated lemon peel
            Cookie dough:
     3/4 c  Sugar
     3/4 c  Oats; quick cooking
     3/4 c  All-purpose flour; u
            -nbleached
     1/2 ts Baking powder
      10 tb Butter; melted
     1/4 c  Milk
     1/4 c  Light molasses
       1 ts Vanilla extract
  
   Recipe by: Jo Merrill
      * butter--unsalted, cut into 1/2 inch pieces, room temperature.
       Filling: Dissolve cornstarch in lemon juice.  Whisk egg yolks, sugar, 4
   tablespoons butter and lemon peel in heavy saucepan. Whisk in cornstarch.
   Whisk over low heat until smooth and thick enough to mound in spoon, about
   5 minutes; do NOT boil. Cool to room temperature, whisking occasionally.
   Add remaining 6 tablespoons butter 1 piece at a time, whisking until
   smooth. Cover tightly and refrigerate until well chilled. This part can
   beprepared 2 days ahead.
   
       Cookies:  Position rack in center of oven and preheat to 350 degrees.
   Dab butter in 3 places on rimless baking sheets or use rimmed sheets turned
   over and dab the butter on the bottom side. Line with foil, leaving 2-inch
   overhang on short ends. Combine sugar, oats, flour and baking powder in
   large bowl.  Add melted butter, milk, molasses and vanilla and stir with
   fork until just blended. Let stand 15 minutes. Drop batter onto prepared
   sheets by heaping teaspoonfuls, forming into 1-inch diameter rounds and
   spacing 3 inches apart. Bake until cookies bubble and begin to brown around
   edges, 6-7 minutes.  Transfer foil with cookies to a work surface. Flatten
   cookies gently with spatula if necessary. Cool completely.
   
       Cookies can be prepared 1 day ahead--store airtight. Just before
   serving, spread 3 teaspoons of filling evenly on bottom side of cookie, top
   with another cookie, bottom side in. Repeat procedure with remaining
   cookies and filling.
  
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