Heat margarine, chocolate, milk and apricot preserves in small saucepan, whisking frequently, until chocolate is almost melted. Remove from heat; whisk in egg yolk and vanilla; mix in combined flour, Equal®, baking powder, and salt until smooth.

 

Beat egg whites and cream of tartar to stiff peaks in large bowl. Fold chocalate mixture into egg whites; fold in walnuts if desired. Pour batter into greased 8-inch square baking pan.

 

Bake in preheated 350 degree F oven until brownies are firm to touch and toothpick comes out clean, 18 to 20 minutes (do not overbake).

 

Cool on wire rack. Server warm or at room temperature.