Line a large sheet pan with parchment paper or a silicone mat. In a very large bowl, add the popped popcorn, miniature marshmallows, and most of the Valentine’s M&M’s. Gently toss everything together so the mix is evenly distributed.
Add the white chocolate chips and ½ tablespoon of oil to a microwave-safe bowl. Heat in 30-second intervals, stirring well between each round, until the chocolate is completely smooth. Pour the melted chocolate over the popcorn mixture and gently toss until coated.
Spread the coated popcorn evenly onto the prepared baking sheet. Melt the remaining chocolate chips with the remaining oil, then drizzle it over the popcorn using a spoon or piping bag. This adds extra flavor and a decorative finish.
While the chocolate is still soft, press the remaining M&M’s onto the popcorn and sprinkle with Valentine’s sprinkles if using. Let the popcorn set at room temperature or in the refrigerator until the chocolate hardens. Break into pieces and it’s ready to serve.