Preheat oven at 180°C (360°F). Line a 20cm x 30cm (8 x 12 inch) slice tin with baking paper.
Using either your stand mixer or hand electric beaters, beat butter and sugar until creamy and pale in colour. Add egg and vanilla and continue to beat until combined.
Add sifted flour, baking powder and stir until completely incorporated.
Spread mixture into slice tin evenly with a smooth surface. The back of a metal spoon works best for this. Once smooth spread jam over evenly.
In a separate bowl add egg whites, sugar and coconut and mix well. Then spread coconut mixture over the top of the slice.
Bake in oven for 35 minutes or until golden brown. Remove from oven and leave to cool in the tin. Once cooled remove from tin and cut into squares to serve. Store in an airtight container.
Cool Completely in the Tin: You may be tempted to remove the slice from the tin before cooling, but it will crumble and break apart. Cool completely before removing from the tin and slicing into portions.Warm the Jam Before Spreading: You don't have to do this step, but if you warm the jam in the microwave it will be easier to spread over the uncooked biscuit base.Line the Tin: Even if you have a nonstick slice tin, make sure to line the tin with baking paper/parchment paper. Leave enough overhang to easily lift the slice from the tin once cooled.GENERAL COOK’S NOTESAll oven temperatures are fan-forced, increase the temperature by 20 Deg C (70 Deg F) for convection ovens.All measurements are Australian tablespoons and cups. All measures are level, and cups are lightly packed unless specified.1 teaspoon equals 5ml1 tablespoon equals 20 ml (Nth America, NZ & UK use 15ml tablespoons)1 cup equals 250ml (Nth America use 237ml)4 teaspoons equal 1 tablespoonI use the below unless specified in my recipes.Herbs are fresh | Vegetables are of a medium size | Eggs are roughly 60 grams in weight (large).NUTRITIONAL INFORMATION BELOW IS A GUIDE ONLY