In a large bowl, beat together butter, brown sugar, 3/4 cup chopped pecans, and vanilla until well blended. Combine flour and baking powder, and stir into the butter mixture. Shape dough into 1 inch balls, and place onto ungreased cookie sheets. Flatten cookies slightly to keep them from rolling off of the pan, and pinch the tops to a point to resemble acorns.
Bake for 10 to 12 minutes in the preheated oven, or until firm. Remove from cookie sheet to cool on wire racks.
In the top of a double boiler, melt chocolate chips, stirring frequently until smooth. Remove from heat; keep chocolate warm over water in the double boiler. Dip pointy ends of cooled cookies into melted chocolate, then into the remaining 3/4 cup chopped pecans. Allow cookies to set on waxed paper.