Preheat oven to 250 degrees.

Heat oil in a large pot over medium heat. Add popcorn kernels and the pot. Shaking pan frequently, cook several minutes, until the popping slows. Once popping has slowed, remove from the heat and allow to sit until popping stops. Pour popcorn into a disposable roasting pan.

Combine sugar, corn syrup, butter, and remaining 1/4 teaspoon of the salt in a medium saucepan over medium heat. Bring to a boil. Cook for 3 minutes, stirring occasionally. Remove from heat and stir in Nutella and vanilla. Stir until Nutella has melted and mixture is smooth. Drizzle over popcorn and stir to coat. Bake popcorn for 1 hour, stirring every 15 minutes. Cool completely before serving.