French Onion Soup Croquettes with Dijon Aioli

Peel the potatoes, cut them into even-sized pieces, and place them in a large pot. Cover with cold water, add a pinch of salt, and bring to a boil. Cook until tender, about 15-20 minutes. Drain well and return to the pot.

While the potatoes are cooking, prepare the caramelized onions. Melt 2 tablespoons of butter in a large skillet over medium-low heat. Add the sliced onions, sugar, salt, and pepper. Cook, stirring occasionally, until the onions are softened and deeply caramelized, about 25-30 minutes. Add thyme during the last 5 minutes. Deglaze with white wine (if using) or broth, scraping up any browned bits from the bottom of the pan. Set aside to cool slightly.

Mash the cooked potatoes with the remaining 2 tablespoons of butter until smooth. Stir in the caramelized onions, Gruyere cheese, salt, and pepper. Mix well to combine.

Allow the potato mixture to cool slightly. Shape the mixture into small croquettes, about 1.5-2 inches in diameter. Place the croquettes on a baking sheet lined with parchment paper and refrigerate for at least 30 minutes to firm up.

While the croquettes are chilling, prepare the Dijon aioli. In a small bowl, whisk together the mayonnaise, Dijon mustard, and lemon juice. Season with salt and pepper to taste. Refrigerate until ready to serve.

Prepare the breading station. Place the flour, beaten eggs, and panko breadcrumbs in separate shallow dishes. Dredge each croquette in the flour, then dip in the egg, and finally coat with the panko breadcrumbs, pressing gently to adhere. Repeat for all croquettes.

Heat the vegetable oil in a large skillet over medium heat until it reaches 350°F (175°C). Carefully add the croquettes to the hot oil in batches, being careful not to overcrowd the pan. Fry for 2-3 minutes per side, or until golden brown and crispy. Remove the croquettes with a slotted spoon and place them on a paper towel-lined plate to drain excess oil.

Serve the French Onion Soup Croquettes warm with the Dijon aioli for dipping.