Preheat oven 180 C / Gas 4. Grease and line 4 (20cm) cake tins.
Mix together sugar, butter and vanilla paste in a large bowl and beat with an electric whisk until pale and fluffy. Add eggs gradually.
Sift flour and baking powder with salt and fold into the cake batter. Pour in milk and beat mixture. Scatter sprinkles and ripple through cake batter before dividing between the cake tins.
Bake until golden, 25 to 30 minutes. Swap the tins around in the oven after 15 minutes to ensure they cook evenly. Cool on wire racks completely before icing.