Sift together flour, baking powder, and salt.
Set aside.
Combine the 1/4 cup (60 mL) of melted margarine and brown sugar replacement in a bowl.
Beat or stir to blend.
Add egg, vanilla extract, and liquid butter flavoring.
Mix well.
Gradually stir flour mixture into margarine mixture.
Lightly grease an 8 x 8 in. (20 x 20 cm) baking pan with vegetable oil spray.
Spread mixture into bottom of pan.
Bake at 350°F (175°C) for 30 minutes, or until top springs backed when touched.
Cool in pan on cooling rack.
Melt semisweet baking chocolate and the 2 tsp (30 mL) of margarine in a small saucepan over low heat.
Cool slightly; then pour and spread over top.
Allow to cool.
Cut into 36 brownies.