Line a cookie sheet with waxed paper or grease-proof paper; set aside.
Put oil in a large saucepan; heat until quite hot. Add popcorn, cover, and cook until popped, shaking most of the time.
Remove from heat, uncover, set aside. Do not season.
Melt both the chocolates separately in the microwave. Set aside.
Pour the melted dark chocolate on top the popcorn. Stir it in until all the popcorn is covered. Turn the popcorn out onto the lined cookie sheet, distributing it evenly. (A spatula may be helpful to clear the pan.)
Then take the melted white chocolate, and drizzle it by spoonfuls over the popcorn.
Let stand at room temperature until chocolate has set again.
You can store this for up to 3 days in a tightly-sealed container.