4 c. flour
1 tsp. baking powder
1 tbsp. cream of tartar
1 c. unsweetened cocoa powder
1/2 c. lard, softened
2 tsp. vanilla
1 1/3 c. sour milk (see note)
1 tsp. baking soda
1 tsp. salt
1 stick butter, softened
2 c. sugar
2 eggs

FILLING:

1/3 c. plus 3 tbsp. flour
1 1/2 c. (3 sticks) butter
2 tsp. vanilla
1 1/2 c. milk
1/4 tsp. salt
3 3/4 c. confectioners' sugar

Preheat oven to 375. Sift together flour, baking soda, baking powder, salt, cream of tartar and cocoa. Set aside.

In large mixer bowl, cream butter, lard, sugar and vanilla together until well blended, about 3 minutes. Add eggs, one at a time, blending after each addition. Add flour mixture to sugar-butter mixture, alternating with milk and beginning and ending with flour. Blend well, but don't overmix. The mixture will look like cake batter and if it appears curdled, don't worry.

Cover cookie sheets with foil. Use 1/4 cup batter each cookie, drop onto cookie sheets-one in each corner, and one in the middle. Make them round as possible. At this point, each cookie will be about 2 1/2 inches in diameter and they should be 3 1/2 to 4 inches apart.

Bake for 6 minutes and, if necessary, reverse cookie sheets from front to back so they bake evenly. Continue baking 10 minutes longer. The only way to tell if they are done is to touch them with your fingertip. If the top of the cookie springs back quickly, remove from the oven; don't overbake.

Slide the foil off the sheet and allow cookies to stand 2 minutes. Remove from foil with metal spatula to waxed-paper covered racks to cool. If any are irregular, trim carefully into rounds with scissors while they are still warm. (Reuse foil.) Repeat with remaining batter until you have 30 cookies.

Meanwhile prepare filling. Place flour in medium saucepan and add milk gradually, whisking smooth. Cook over moderate heat, cooking and whisking until mixture becomes thick and bubbles in center. Simmer over low heat for 2 minutes. Remove from heat and set aside to cool.

Place the butter in large mixer bowl and beat until slightly softened. Add salt, vanilla and sugar gradually and beat for 2 minutes. Gradually one large spoonful at a time, add the cooled milk mixture to the butter mixture. Then beat on high speed for 1 minute until filling is smooth, light and fluffy. If the filling seems too soft, refrigerate until it firms up a bit.

Arrange cookies in pairs flat sides up. Place generous 1/4 cup filling on 15 of the cookies, using all of the filling. Spread filling to about 1/2 inch from edge; it will be almost 1/2 inch thick. Top with another cookie, flat side down. Press cookies together so filling comes to edges.

Chill, then wrap each cookie individually in plastic wrap. Store in refrigerator, but they taste better eaten at room temperature. They also freeze very well. Makes 15 very large cookies.

Note: To make sour milk, add 1 tablespoon plus 1 teaspoon cider vinegar to 1 1/3 cups regular milk and let stand 1/2 hour.