Baking without baking powder or baking soda?

Vanilla slices. 125g butter, chopped--200g Dark Chocolate chopped coarsely--1/2 cup (110g) caster sugar--2 eggs beaten lightly--1 1/4 (185g) plain flour--1 1/2 cups (240g) icing sugar--mixture--1 teaspoon butter, extra--2 tablespoons milk, approximately.--1/4 teaspoon vanilla essence.--50g dark chocolate, melted, extra.----------------------Preparation time 20 minutes. Cooking time 30 minutes.---------------------------1. preheat oven to moderate. Grease deep 19cm-square cake pan; line base with baking paper-------2. combine butter and chocolate in medium sauce-pan; stir over low heat until chocolate melts. Stir caster sugar and egg then flour. spread mixture in prepared pan.; bake in moderate oven about 20 minutes. Stand cake in pan 15 minutes; turn onto wire rack to cool.-----Meanwhile combine icing sugar, extra butter and essence in small heatproof bowl; gradually stir enough milk to make mixture form a thick paste. Stir mixture over small saucepan of simmering water until icing is of spreadable consistency. Spread icing over cake; allow to set at room temp.------4 using knife, trim crisp edges from cake. cut cake into 3 cm squares; drizzle each square with melted chocolate.