Heat oven to 180C/fan 160C/gas 4.
Melt half the butter in a large cast-iron
casserole over a medium heat, add
the onions, then fry for 8-12 mins until
golden, stirring occasionally. Add the
garlic just before the end, then transfer
everything to a bowl. Turn the heat up
a little, season the beef with salt and
pepper and seal it in batches so as not to
overcrowd the pan, adding a knob of the
remaining butter with each one. Deglaze
the pan with a little stock as you go along.
Return the onions and beef to the pan,
sprinkle over the flour, stir, then pour over
the Guinness and stock. Add the herbs,
sugar, vinegar, mushroom ketchup (if using)
and some seasoning. Bring the liquid to
the boil, cover, then cook in the oven for
1½ hrs. If serving on the day, skim the fat
off at this stage.
Remove the casserole and turn the
oven up to 200C/fan 180C/gas 6. Discard
the herbs, check for seasoning, then
add the celery. Mix the remaining butter
with about 2 tsp Marmite, then spread it
over the slices of French bread on one
side. Arrange the slices, Marmite-side up,
overlapping on top of the casserole, then
return to the oven for another 30-40 mins
until the toasts are golden and crisp.
Serve straight away.