1. Preheat oven to 375 degrees F (190 degrees C). 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.
2. 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.
3. Bake for 10 to 12 minutes in the preheated oven, or until firm. Remove from cookie sheet to cool on wire racks.
4. 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.