Popcorn Vanilla Bean Fudge

Popcorn Vanilla Bean Fudge
15g (1 tbsp) cold unsalted butter, plus more for pan
1 1/2 cups pouring cream
3 cups sugar
1/4 cup liquid glucose or light corn syrup
1/4 teaspoon salt
1 tsp pure vanilla extract or vanilla bean paste
1/2 cup popping corn kernels, popped

Grease an 20cm square baking pan; line with parchment paper, allowing a 3cm overhang. Grease parchment paper, and set aside. Put butter into a large bowl, and set over a wire rack; set aside. Gently heat cream in a large saucepan with 3/4 of the popped popcorn (set some aside to top off the fudge). Simmer for about 10 mins but do not allow the mixture to come to the boil. Strain mixture. Put popcorn cream, sugar, glucose, vanilla and salt into a medium heavy saucepan.

Cook over medium-low heat, stirring constantly, until sugar has dissolved, about 10 minutes. Raise heat to medium. Bring mixture to a boil, washing down sides of pan with a wet pastry brush to prevent sugar crystals from forming. Attach a sugar thermometer to pan; continue to cook, without stirring, until mixture registers 238 degrees F(115 degrees C, soft-ball stage), 10 to 15 mins.

Immediately pour mixture into bowl with butter (do not scrape out the bottom of the pan). Attach thermometer to bowl. Let mixture cool, undisturbed, until it registers 110 degrees F (43 degrees C), about 1 1/2 hours.

Remove thermometer. Transfer bowl to a work surface. Using a wooden spoon, begin to gently stir mixture.Continue to stir, gradually increasing speed until mixture thickens, lightens in color, and loses its sheen, 4 to 5 minutes.

Pour into prepared pan. Using a small offset spatula, quickly spread fudge to sides of pan, and smooth top. Sprinkle an even layer of (lightly salted) popcorn over the top of the fudge. Let fudge cool in pan on a wire rack, about 1 hour. Cover with plastic, and refrigerate untilcompletely set, about 8 hours. Run a sharp knife around nonparchment sides to loosen; lift fudge out. Cut into small square pieces (it's rich so the smaller, the better).