Gravy doesn't thicken cottage pie

[Em2122]

I always fail at making cottage pie. I reduce the stock but it doesn't really thicken it just boils away . What am I doing wrong?
I use flour on the mince, I use 5% mince is that the reason why?

I used the BBC good food shepherds pie recipe this week. There was no flour at all & gallons of liquid. I had to boil.it down for ages & added cornflour.

Bistro and ketchup.

I suspect you are not using enough flour.

Don't put liquid stock in at all. I use a stock cube crumbled in when browning the mince, then you can either have it dry (add veg - peas and carrots minimum) with the mash on top or if you want gravy, make up Bisto or in a pinch, packet casserole mix, with less water than directed so it's gloopy.