Make the bechamel sauce: Put the cake flour and margarine in a heatproof dish and microwave for 1 minute. Add a little milk and mix.
Microwave for 2 minutes → mix → microwave for 3 minutes. Add the soup stock granules, salt and pepper to season. Leave to cool down a bit.
Make the meat pie filling: Cut the kabocha squash into small pieces, put in a heatproof container and microwave for 4 minutes. Mash.
Finely chop the onion and garlic.
Put margarine in a frying pan and sauté the onion and garlic. When the color changes, add the ground meat.
Add the flavoring ingredients. Add the milk and cook until the moisture has evaporated. Turn off the heat, and mix in the mashed kabocha squash.
Put the mixture in a gratin dish, and cover with the bechamel sauce.
Make the pie: Cut the frozen pastry sheet to fit the size of the gratin dish, and place it on the gratin dish as a lid over the fillings. Press the edges down with a fork to prevent the sauce from spilling out.
Brush the top with egg yolk, and place 1cm strips of pastry in a diagonal pattern on top.
Brush with egg yolk again. Cut out a fish shape from the reamining pastry and place it on the pie. Brush the whole top thinly with egg yolk.
Bake in a preheated 190C oven for 15 to 20 minutes, and it's done.