Preheat oven to 375˚F. In a large pot, heat the olive oil over medium heat. Add the onion, carrots, celery, garlic, and the thyme sprig. Sauté, while stirring, until the vegetables start to soften, about 3-4 minutes. Add the jackfruit and cook for 2 minutes, stirring often. Remove the vegetables to a bowl and set aside. 

In the same pot, melt the butter. Add the flour and whisk until the mixture starts to turn gold, about 1-2 minutes. Add the warm milk slowly, while whisking, ensuring the mixture thickens. Add the broth and whisk. Add the garlic powder, the onion powder, the fresh thyme, the nutmeg, and the sea salt and pepper. 

Add the vegetables back to the pot, as well as the green peas. Heat through. Place the mixture in a 8 x 11 1/2-inch baking dish. On a lightly floured work surface, roll out the puff pastry sheet to a 9 x 13-inch rectangle. Lay the pastry over the baking dish and gently tuck in the overhanging pastry. Using a sharp knife, cut 4 slits in the top of the pastry. Brush the top of the pastry with the melted butter or vegan ghee, and set the pie on a rimmed baking sheet. Place in the oven and bake for about 1 hour, until the puff pastry is golden brown and the filling is bubbly. Let stand for 30 minutes before serving. Bon appétit!