Mix lotus seed paste and walnuts together in a bowl; set aside.
Sift flour, milk powder, baking powder, and salt together into a bowl. In large bowl of electric mixer, beat eggs on medium speed until light and lemon colored. Add sugar; beat for 10 minutes or until mixture falls in a thick ribbon. Add melted shortening; mix lightly. With a spatula, fold in flour mixture. Turn dough out on a lightly floured board; knead for 1 minute or until smooth and satiny. Divide dough in half; roll each half into a log. Cut each log into 12 equal pieces.
To shape each moon cake, roll a piece of dough into a ball. Roll out on a lightly floured board to make a 4-inch circle about 1/8-inch thick. Place 1 tablespoon of lotus seed paste mixture in center of dough circle.
Fold in sides of dough to completely enclose filling; press edges to seal. Lightly flour inside of moon cake press with 2-1/2 inch diameter cups. Place moon cake, seam side up, in mold; flatten dough to conform to shape of mold. Bang one end of mold lightly on work surface to dislodge moon cake. Place cake on ungreased baking sheet. Repeat to shape remaining cakes. Brush tops with egg yolk.
Bake in a preheated 375 degree F. oven for 30 minutes or until golden brown. Transfer to a rack and let cool. Makes 2 dozen