Beat eggs, one at a time, into brown sugar mixture. Add vanilla. Combine flour, baking powder and salt; beat in until blended. Stir in walnuts and 1/4 cup of the chocolate morsels. Spread mixture in baking pan, and sprinkle remaining chocolate morsels on top.

Place pan in oven for 3 minutes. Remove pan and lightly run a knife through batter a few times so chocolate forms a marble pattern. Quickly return pan to oven and bake 30 minutes longer. Let cool completely. Then cut into 15 blondies.