Peel the apple and cut into dice. In a pan, heat some olive oil and cook the apple on medium heat for about 15 minutes. The apples should get “creamy." Remove from heat and add the nuts and thyme leaves
Preheat oven on 350F
Cut the brie into slices
Roll out the puff pastry and make four rounds. Spread the rounds into four individuals pie pans. Prick the bottom with a fork, spread one teaspoon of mustard on each tartlet then add the apples and nuts mixture
Cover with slices of brie (If you have some pastry left you can decorate the top with strips of puff pastry). Add a a sprinkle of olive oil, salt and pepper
Bake for about 25 minutes. You may have to cover the pies with aluminum foil if the tartlets start getting too brown.