In a dozen to 36 cm saute pan, heat olive oil until smoking. Add onion, garlic and fennel seeds and saute until light golden brown. Add pork, season with salt and cook until lightly browned. Add vinegar, sugar, tomato sauce and wine and bring to a boil. Lower heat and simmer 1 hour, until very tender. Remove from heat and allow to cool. In a mixing bowl, place cooled pork mixture, mint, 2 eggs, pecorino and parsley and stir to combine. Set aside.
Mix flour and semolina together in a mixing bowl and make a well. Add water-butter mixture and stir to form a ball of dough. Remove dough from bowl and place on work surface. Knead for 1 minute, wrap in plastic and refrigerate 1 hour.
Preheat oven to 220ºC and line a cookie sheet with parchment.
Roll out dough to 1 cm thick and cut out 15 cm circles. Place two to three tablespoons of pork mixture in each one and fold to form a half moon. Seal edges, pressing with fingertips and place on lined baking sheet. Continue until all the dough is used up. Beat remaining 2 eggs and brush each impanada with the egg wash. Bake for 30 to 40 minutes, until golden brown and remove. Serve warm with a marinated tomato salad.