Mince meat.
That's all you need to know
For reference, the bottom of the pie is made with suet pastry, so it it soft and sinks into the liquor. Only the top is short crust.
It has a distinctive flavour - I would recognise a Pie and Mash shop pie blindfold. I think it helps to grow up with it - the lady at the Post Office said she had hers with gravy and ketchup because "I didn't grow up round here". I shuddered.