Heat oil over medium heat and add the garlic, fennel seeds and thyme until aromatic for 1 minute. Add onion and celery, cook for 5 minutes. Add carrots and cook 20 minutes or until mushy. Remove from heat and let cool.
Put the ground pork in a large bowl and add the cooled veggies, breadcrumbs, salt and white pepper. Using your hands, mix well.
Preheat oven to 400 degrees. Roll the puff pastry (that you bought) into a rectangle. Cut the pastry into 6 rectangles for about 6×12 inches each.
Divide the filling mixture into 6 even-sized portions. Roll each portion out into a 12-inch long log (like a sausage without the casing). It should be about 1 1/4 inches in diameter. Place each log lengthways in the centre of the pastry rectangle and brush one long edge with egg wash.
Firmly fold the pastry over, pressing to enclose the log tightly, leaving the ends open. Cut each roll into 2 even-sized pieces and place them on a baking tray lined with baking paper. Brush the top of each roll with egg wash and sprinkle with fennel seeds.
Reduce the oven temperature to 375 degrees Fahrenheit and bake for 35 to 40 minutes or until they are a golden brown roll of steaming oozing goodness. It sounds harder than it is.