Prepare the mushroom filling: Heat olive oil in a pan. Sauté shallot and garlic for 1 minute. Add mushrooms and thyme. Cook until dry. Season with salt and pepper. Let cool.
Assemble the Wellington: Roll out puff pastry. Place cooled mushroom mix in the center. Fold and seal edges. Brush with egg wash or plant milk.
Bake: Preheat oven to 400°F (200°C). Bake for 25–30 minutes until golden brown.
Make the jus: Simmer pomegranate juice and vinegar until reduced by half. Stir in honey or molasses. Season lightly with salt.
Wilt the spinach: Heat olive oil in a skillet. Add garlic, cook 30 seconds. Add spinach and stir until just wilted. Season with salt.
Serve: Slice the Wellington. Plate over spinach. Drizzle with pomegranate jus.