Grease the mould with the butter. Roll out the dough to a thickness of about 1⁄8 to ¼ in (4 to 5mm), then line the mould with the dough, going all the way up the sides.
Scrape the filling into the mould (do not fold the dough over the top).
Preheat the oven to 400°F (200°C).
Bake the pâté for about 25 minutes, or until beautifully golden brown, then lower the oven temperature to 275°F (140°C) and bake until the centre reaches 149°F (65°C) on the instant-read thermometer.
Meanwhile, make the gelée. Melt the gelatin in the warm broth, then stir in the port.
Remove the pâté from the oven and fill it with the warm gélee.
Repeat this step four or five times in about 30-minute intervals.
Refrigerate the pâté and any remaining gelée overnight.