In a microwave-safe mug, combine the white chocolate and the oil. Microwave for 30 seconds to 1 minute, until chocolate is melted. Stir to combine completely.
Stir in the milk, sugar, and vanilla. Then stir in the flour, baking powder, and salt until everything is completely combined. (If it feels a bit thick, add in some more milk. If it feels too runny, add in a bit more flour. You want it to be like a simple cake batter.) Stir in the raspberries reserving 3 for garnish.
Microwave the cake for 90 seconds. Take it out and check if it’s done. Too gooey? Pop it back in for 30 second intervals until it’s just how you like it. Top with remaining 3 raspberries and any leftover white chocolate shavings.