Pre-heat oven to 375 degrees Fahrenheit.
In a skillet over medium-high heat, brown beef and onion then stir in the vegetables, thyme, Guinness, Worcestershire sauce and seasonings then bring to a boil.
Reduce heat and simmer for 7-8 minutes or until vegetables are tender.
Spoon filling into bottom pastry shell, brushing the edges with milk, cover with top shell and then press with a fork to seal.
Bake 20-22 minutes or until pastry is golden and flaky. Serve warm.