Preheat oven to 300 degrees. Butter a large rimmed baking sheet, set aside. Place popcorn in a large bowl and said aside.
In a small saucepan, bring butter, sugar, and 2 tablespoons water to a boil, stirring constantly. Working quickly, drizzle popcorn with sugar syrup, and toss to coat.
Spread popcorn evenly on prepared baking sheet. Sprinkle with coarse sea salt. Bake, tossing occasionally, until golden and shiny, about 40 minutes. Transfer hot popcorn to parchment-paper-lined baking sheet; let cool.
Once popcorn is cooled, melt the chocolate. Place semi sweet chocolate chips in a microwave safe bowl. Microwave on half power for 2 minutes. Stir, then return to microwave and heat for another 20 seconds at a time, stirring between each, until smooth. Drizzle over popcorn. Repeat process with white chocolate. Allow to cool until chocolate is hardened. Store in airtight container.