Steps

Place all of the ingredients into a medium saucepan over a high heat. Whisk well to combine, then bring to the boil. Reduce the heat to low and simmer for 10 to 15 minutes, or until it's sticky and coats the back of a spoon. 

Steps

1. Heat oil in a saucepan over medium heat. Place apple pieces in saucepan; cook and stir until they are slightly caramelized, about 2 minutes.
2. Stir brown sugar into apples; cook, stirring constantly, until the mixture starts to bubble, about 2 minutes.
3. Pour apple cider vinegar into saucepan. Reduce heat to low and cover. Cook until the apples are soft and falling apart, about 30 minutes. Remove from heat.
4. Whisk in mustard, red pepper flakes, and black pepper.
5. Transfer mixture to blender and puree until completely smooth.