Heat the butter and olive oil together in a large frying pan set over a medium heat. Sweat the onion with some seasoning for 8-10 minutes, stirring occasionally, until it starts to soften. Sprinkle over the caster sugar, reduce the heat to low and continue to cook for 15-20 minutes, stirring occasionally until lightly caramelised. Remove from the heat and set to one side.
Preheat the oven to 220°C.
Combine the flour, salt, yeast and sugar in a large mixing bowl. Mix in the oil and water to form a dough, bringing it together with your hands, then kneading gently on a lightly floured surface for a few minutes until even. Roll out into a 45cm x 15cm oval shape.
Arrange on a baking tray then spoon the caramelised onions evenly on top. Position the rounds of goat's cheese spaced evenly apart on top of the onions and bake in the oven for 18-22 minutes until the base is cooked and golden-brown in colour.
Remove and allow to stand for a few minutes before serving.