Caramel feijoa upside down cake

Topping

• olive oil spray, for greasing
• 100 g unsalted butter, cut into pieces
• 150 g brown sugar
• 1 tsp natural vanilla extract
• 3 - 6 feijoas, trimmed, peeled and cut into slices (1 cm - see Tips)

Cake

• 70 g unsalted butter, softened
• 100 g caster sugar
• 200 g plain flour
• 1 tsp ground ginger
• 1 tsp ground cinnamon
• 150 g milk
• 50 g natural yoghurt
• 1 tsp bicarbonate of soda