Step 1: Roast the Sweet Potatoes

Start by preheating your oven to 400°F (200°C). While the oven is heating up, peel and cube the sweet potatoes. Place them on a baking sheet, drizzle with 1 tablespoon of olive oil, and sprinkle with a pinch of salt and pepper. Toss to coat the potatoes evenly.

Roast the sweet potatoes in the preheated oven for about 25 minutes, or until they are fork-tender and slightly caramelized. For an added depth of flavor, you can toss the sweet potatoes with ground cumin and fresh thyme before roasting. Once done, remove them from the oven and set aside to cool.

Step 2: Caramelize the Onions

While the sweet potatoes are roasting, heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the thinly sliced onions and sauté them, stirring occasionally, until they begin to soften and caramelize—this will take about 15-20 minutes. You want the onions to become golden brown and sweet, so be patient and don’t rush this step!

Once the onions are caramelized, drizzle them with 1 tablespoon of balsamic vinegar (optional), and season with salt and pepper to taste. This will add a bit of tanginess and extra flavor to the filling.

Step 3: Combine the Filling Ingredients

Once the sweet potatoes have cooled slightly and the onions are caramelized, it’s time to assemble the filling. In a large mixing bowl, combine the roasted sweet potatoes and caramelized onions. Use a fork or potato masher to mash the sweet potatoes slightly, but leave some chunks for texture.

Stir in the fresh thyme and adjust the seasoning with more salt and pepper, if needed. If you’re adding spinach, cheese, or grains, now is the time to mix them in. The spinach will add freshness, the cheese will bring a creamy, tangy element, and quinoa or lentils will provide extra texture and protein.

Step 4: Prepare the Puff Pastry

Roll out the puff pastry sheets on a clean, lightly floured surface. You want the sheets to be large enough to encase the filling, so if necessary, gently press the seams of the two sheets together to form one large rectangle.

Transfer the prepared filling onto the center of the pastry, spreading it out into an even line. Leave about 1 inch of space on the sides to allow for folding.

Step 5: Assemble the Wellington

Carefully fold the sides of the puff pastry over the filling, tucking the edges in and sealing it shut. Use a fork or your fingers to press the edges and seal them. You want to make sure the Wellington is tightly sealed so that the filling doesn’t leak out while baking.

Once the Wellington is sealed, turn it over so the seam side is facing down. If desired, use a sharp knife to lightly score the top of the pastry to create a decorative pattern. This will help the pastry cook evenly and give it a beautiful presentation.

Step 6: Apply the Egg Wash

Brush the top of the Wellington with the beaten egg to give it a golden, glossy finish when baked. This will also enhance the flaky texture of the puff pastry.

Step 7: Bake the Wellington

Place the assembled Wellington on a baking sheet lined with parchment paper. Bake it in the preheated oven at 400°F (200°C) for about 25-30 minutes, or until the puff pastry is golden brown and crispy.

Keep an eye on the Wellington as it bakes to ensure the pastry doesn’t burn. If it begins to brown too quickly, you can cover it loosely with aluminum foil and continue baking.

Step 8: Rest and Serve

Once the Wellington is baked to perfection, remove it from the oven and let it rest for about 5-10 minutes before slicing. This resting time allows the filling to set and makes it easier to slice without spilling.

Slice the Wellington into thick, hearty slices and garnish with fresh herbs like parsley or rosemary for a burst of color and freshness.