Prepare the 3.9 oz (1 bag) microwave popcorn according to package instructions (use plain or lightly salted popcorn, not butter-flavored). Open carefully and pour the popped popcorn into a large bowl; remove any large unpopped kernels. Set the bowl aside.

Place 10 Oreo cookies (113 g) in a resealable plastic bag and crush into small pieces with a rolling pin or pulse briefly in a food processor. Set the crushed cookies aside.

Put 1½ cups (255 g) white chocolate chips and 2 tsp (8 g) canola oil in a small microwave-safe bowl. Microwave for 30 seconds, stir, then continue microwaving in 30-second increments, stirring between each, until the white chocolate is fully melted and creamy (about 1–1½ minutes total). Stir thoroughly to combine.

Pour the melted white chocolate over the popcorn. Use a large spoon or spatula to fold and stir the popcorn until it is as evenly coated as possible. Work quickly while the chocolate is still wet.

Spray a large baking sheet with nonstick spray or line it with parchment paper. Spread the coated popcorn onto the prepared baking sheet in an even layer.

Immediately sprinkle the crushed Oreos over the popcorn and add extra white chocolate chips for garnish, if desired.

Place the baking sheet in the refrigerator for about 20 minutes, or until the chocolate has hardened.

Use a spatula to break the popcorn into clusters and transfer to an airtight container for storage until ready to serve.