Tunnock’s teacake traybake

Method

1. Heat the oven to 180°C/160°C fan/gas 4. To make the base, pulse the oatmeal, flour, salt, baking powder and sugars in a food processor, add the butter and pulse to breadcrumbs. Add the milk and whizz until the mixture comes together. Alternatively, mix the dry ingredients in a bowl, then rub in the butter and use a knife to stir in the milk.
2. Tip into the tin, then use the back of a metal spoon to press it down and smooth the top. Bake for 25 minutes or until the biscuit has come away from the edges of the tin and feels firm to the touch. Cool in the tin set on a wire rack.
3. Put all the meringue ingredients in a large heatproof bowl set over a pan
   of simmering water (don’t let the bowl touch the water). Using an electric hand mixer, whisk the mixture for 6-8 minutes until thickened – the mixture must be very stiff to hold its shape. Spoon over the cooled biscuit base.
4. Leave the meringue to set, then pour over the melted chocolate, smoothing
   it over with the back of a spoon. Leave in a cool place to set, then use a hot sharp knife to cut into 16 rectangles.