OK, I'm between brownie pans and had to improvise with a muffin pan. These are normally tray baked and iced before being divided into squares, which are cut in half diagonally to make long triangles. They look and taste better in triangular form, but needs must.
These seem to have been a specialty unique to my school's dinner ladies, i've never met anoyone else who has eaten them. I remember being in sixth form and discussing with my friends how we would ever live without eating two of these things a day for rest of our lives, though it turns out that moving away to university offers plenty of other interesting distractions. I didn't give them a second thought, until I was thrust into proper adulting with a family and baking duties.
Thankfully some enterprising soul got the recipe from a retired dinner lady and it periodically does the rounds on my Facebook feed - complete with catering quantity measurements. Its a nice thrifty treat - and its very good for school bake sales. The original recipe uses butter, I use vegan margarine or coconut oil. I've also cut the quantities down to household size.
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175g porridge oats
175g plain flour
125g caster sugar
2 tbsp cocoa powder
1 1/4 tsp baking powder
175g icing sugar
2 1/4 tbsp cocoa powder
Preheat oven to 180∘ and bottom line a 9" x 9" brownie pan.
Cream the margarine in a large mixing bowl.
Sift the sugar, flour, cocoa and baking powder into the margarine and add the oats.
Gradually mix the dry ingredients into the margarine.
Spread mixture into the brownie tray and bake for 30-40 mins until top is firm to touch.
Remove from the oven and allow to cool completely in the tray before icing. Some collapse on cooling is normal.
Sift together the icing sugar and cocoa. Stir in the boiling water tablespoon by tablespoon until the consistency is a little thicker than single cream.
Spread the icing over the cooled traybake and allow to set.
Cut into squares, and then diagonally into triangles.