It's moist, not too sweet and it's an interesting-looking addition to the tea table thanks to the burst blueberries all over the surface.
135 g caster sugar
90 g butter
58 ml extra virgin olive oil
78 ml milk
half teaspoon vanilla extract
200g plain flour
three quarters teaspoon baking powder
pinch of salt
zest of 2 lemons
zest of 2 oranges
150g blueberries (more or less to taste)
Beat the eggs and sugar for a couple of minutes until they're yellow and thick.
Whilst you're doing this, melt the butter over a low heat, then stir it into the eggs/sugar mixture.
Stir in the olive oil, milk and vanilla. It'll bubble pleasantly.
Sift in your flour, baking powder and salt, stirring thoroughly without paying attention to any lumps or bubbles, as these will disappear.
Put a tea-towel over the bowl and set aside for 10 minutes whilst you zest the lemons & oranges. (The flour needs time to absorb the liquid.)
Stir in the zest, then half of the blueberries.
Turn into a lined & buttered tin. You have a couple of options - for a traditional-looking English cake, served as hefty triangular wedges, put in a 6 inch (or thereabouts) round tin - a springform one is most helpful. Or for a slightly more modest-looking offering, put in a much wider tin, perhaps a square one, to get thinner, flatter slices.
Bake at 175 degrees C (that's 350 F or gas 4 or wherever your Aga does cakes best) for 15 minutes.
Take out, then gently push the remaining blueberries into the top of the cake - you may have to break the surface around the edges where the cake has begun to set.
Bake for another 30 - 40 minutes.
Leave to cool on a rack for 10 minutes before turning out.