Slow Cooker Steak Pie with cheddar

puff pastry circle sheet (10 inches diameter) (home made or frozen)

brown onion (finely sliced)

+ 2 tbsp red wine ((150 ml))

diced rump steak ((500 g))

cheddar cheese ((150 g))

beef stock ((500 ml))

cornstarch

Salt

ground pepper (optional)

egg

water