Whip up the butter with the sugar, salt and oil until the mix becomes lighter. You can do this with an electric mixer or using a hand-held whisk.
Add the eggs and beat them again until they are fully incorporated and the mix looks airy. From all the whipping, the mix should thicken and start to unstick from the sides of the bowl.
Add the milk and oassion fruit juice and mix. It will look split, but don't worry. It will come back with the flour.
Add the flour and baking powder and mix.
Paint the pan with very little melted butter at a time and make sure to go into all the little edges of it. Flour the pan and give it little taps as you rotate it to cover it completely. Then turn it over and give it a few taps on the counter so the excess flour drops.
Place the batter inside the mould and spread it out. You also want to use a small spatula or the back of a spoon to go around the pan and make the centre of the dough be a bit deeper so that when it bakes it fills up to a plain.
Bake the cake at 180°C/350°F for 40min-1hour or until a knife comes out clean. It's important to not overcook it to prevent it from drying out. If you have an electric oven, check the cake at the 30-minute mark. If it's golden enough on top, change the heat source to only the bottom.
Unmould the cake while it's still hot.