Defrost 3 sheets flaky puff pastry. Spray a round pie dish or baking dish with oil spray. Preheat the oven to 200 °C fan bake. Line an oven tray with baking paper.
Cook filling
Peel and finely dice ½ brown onion. Peel and mince 4 cloves garlic. Heat 1 tbsp olive oil in a large frypan on medium-high heat. Cook the onion and garlic for 2 minutes. Add 500 g beef mince and cook for 4 minutes, breaking up the lumps with a wooden spoon. Add ¼ cup tomato paste and crumble in 1 cube beef stock and cook for 2 minutes.
Make pie
Line the prepared pie dish with the defrosted pastry, ensuring up the sides is covered. Spoon the filling into the dish and smooth out. Layer over 40 g gherkins, evenly spread over ¼ cup burger sauce, and grate over 100 g cheddar cheese. Place a final sheet of flaky puff pastry over the top and pinch the edges with your fingers or use a fork to crimp. Whisk 1 egg in a small bowl, then brush it over the pastry. Sprinkle over 1 tbsp sesame seeds.
Bake pie
Bake the pie in the oven for 20-25 minutes or until the pastry is golden and cooked.Tip: If you're making individual pies cook for 15-20 minutes. For one family-sized pie cook for 20-25 minutes.
Bake fries
Cook 750 g frozen shoestring fries on the prepared oven tray according to packet directions. Tip: Time it so they finish cooking at the same time as the pie.
To serve
Slice and divide the Big Mac pie between plates. Serve with the shoestring fries and tomato sauce on the side.