Pop the popcorn and prepare your work surface. Pop your kernels in a large pot with a little oil, or use a popcorn machine. You should have about 100 g of popped corn. Remove any unpopped kernels (you'll hear them clatter against the pan) and place the popcorn in a very large mixing bowl – it should be big enough to stir without kernels flying out. Lightly butter a baking tray or line it with parchment paper.

Melt the marshmallow base. In a large saucepan over low heat, melt the butter until it hisses gently, then add the marshmallows and golden syrup. Stir continuously with a wooden spoon – the marshmallows will first look puffed and opaque, then collapse into a glossy, thick liquid after about 3–4 minutes. You'll smell a sweet, vanilla-like aroma. Remove from the heat immediately and stir in the salt and vanilla extract.

Combine popcorn and candy corn. Pour the hot marshmallow mixture over the popcorn. Sprinkle in the candy corn and peanuts (if using). Use a silicone spatula or a well-buttered wooden spoon to fold everything together. At first the mixture will feel sticky and stringy – keep folding until every piece of popcorn is coated and the candy corn is evenly distributed. Work quickly before the marshmallow sets.

Shape the balls while still warm. Lightly butter your hands (or wear food-safe gloves) to prevent sticking. Scoop up about a handful of the mixture – roughly 70–80 g – and press it firmly between your palms to form a ball. The mixture will be warm but not burning. Compress it just enough to hold its shape; you should see pieces of candy corn studding the surface. Place each ball onto the prepared tray. Repeat with the remaining mixture.

Cool and set. Let the popcorn balls sit at room temperature for at least 25 minutes. As they cool, the marshmallow will firm up and the balls will become stable. You can check by gently pressing one – it should feel slightly springy but not sticky. If you try to bite into one too soon, the candy corn will still be soft and pull apart.

Serve or store. Once fully set, arrange the balls on a platter or wrap individually in cellophane bags for party favours. They will keep in an airtight container at room temperature for up to 5 days – though the popcorn may soften slightly over time.