Heat 4 tablespoons of olive oil in a pan and add salt, black pepper, and the leek. Cook for about 5 minutes while stirring, then remove from heat.
Place parchment paper on a baking sheet, sprinkle it with honey and 2 tablespoons of olive oil. Arrange the sweet potato slices on it, and add the cooked leek on top. Cut the puff pastry into a circle and poke holes in it with a fork; then, place it on top of the leek. Bake for about 45 minutes.
Transfer it onto a plate and sprinkle a little thyme.