Heat oven: 170c fan. Line 9×13” tin.
Beat: Butter + sugar for 4–5 mins.
Add: Oil, then eggs + vanilla.
Mix: Flour + cornflour + baking powder + salt.
Fold: Dry mix into wet, alternating with milk + sour cream.
Bake: 35mins.
Cool completely.
Mix icing sugar + vanilla + milk.
Add a little more milk until thick and spreadable.
Spread over cake.
Add hundreds & thousands.
