Chicken and Mushroom Wellington

Preheat oven to 400°F (200°C). Place chicken breasts on work surface. Slice lengthwise through centre of each breast, without cutting all the way through. Open up like a book; place sheet of plastic wrap on top. Using meat mallet or rolling pin, flatten into 1/2-inch (1 cm) thickness. Season with half of the salt and pepper; set aside.

Heat half of the oil in large skillet set over medium-high heat; cook mushrooms, onion and garlic for 13 to 15 minutes or until onion and mushrooms are tender and browned and moisture has evaporated.

Add wine; cook for 2 to 3 minutes or until pan is almost dry. Add spinach; cook for about 1 minute or just until starting to wilt. Reduce heat to low. Stir in cream; simmer for 5 to 8 minutes or until thickened and creamy. Season with remaining salt and pepper.

Spread mushroom mixture evenly over butterflied chicken breasts, leaving 1-inch border along edges and roll up to enclose filling. Heat remaining oil in large skillet set over high heat; sear rolled chicken breasts, turning occasionally, for 2 to 3 minutes per side or until evenly browned. Let cool completely.

Brush mustard over puff pastry sheets. Place 1 chicken roll on each piece of puff pastry; roll up to enclose, tucking in edges and pinching to seal. Transfer seam side down to parchment paper–lined baking sheet. Refrigerate for 30 minutes.

Brush pastry with egg; bake for 25 to 30 minutes or until pastry is golden, flaky and internal temperature of reaches 165°F (74°) on instant-read thermometer inserted in centre of chicken. Let cool slightly before slicing.