Sausages en Croûte with Caramelized Onions and Crispy Gruyère

In a large nonstick fry pan over medium heat, warm the oil. Add the onions, season lightly with salt and pepper and cook, stirring occasionally, until very soft and caramelized, about 25 minutes. Transfer to a bowl and let cool to room temperature.

Position 1 rack in the upper third and 1 rack in the lower third of an oven and preheat to 400°F. Line 2 baking sheets with parchment paper.

Lay the puff pastry sheets so the folded seams are parallel to you. If necessary, lightly roll each sheet so it is 10 inches wide. Cut each sheet along the 2 seams to create 3 pieces. Then cut each piece crosswise into 10 pieces, each 1 inch wide.

Place a small amount of caramelized onions along the center of each puff pastry strip. Place a piece of cheese toward the bottom of the strip, perpendicular to the strip so the edges of the cheese stick out of the sides. Place a piece of sausage on top of the cheese. Roll the dough around the sausage and cheese and pinch the seam to seal. Transfer, seam side down, to a prepared baking sheet. Repeat with the remaining puff pastry strips, caramelized onions, cheese and sausages, spacing the sausages en croûte about 1 inch apart on the baking sheets. Brush the tops with the egg mixture.

Bake until the cheese is crispy on the edges and the puff pastry is evenly golden brown, about 25 minutes, rotating the baking sheets from top to bottom and 180 degrees halfway through baking. Let cool for 10 minutes.

Serve the sausages en croûte with cornichons and mustards alongside. Makes 60 sausages en croûte.