Preheat your oven to 200°F and line two large rimmed baking sheets (18" x 13") with parchment. Pour the popped corn into a large bowl (at least 6 quarts); remove any unpopped kernels. Set aside., In a 3-quart saucepan over medium-high heat cook the molasses, brown sugar, butter, and corn syrup, stirring occasionally until the sugar dissolves. Boil the syrup, stirring occasionally, for 5 minutes until it reaches 250° to 255°F on a digital or candy thermometer. The syrup will darken slightly., Remove the pan from the heat and add the baking soda; stir well (the mixture will foam)., Immediately (and carefully) pour the hot syrup over the popped corn and stir until the corn is well coated., Spread the hot caramel corn on the sheet pans. Bake at 200°F for 1 hour, stirring every 15 minutes., Remove from the oven and let cool before storing in an airtight container. This recipe doubles and triples well.