Stout-Braised Short Rib Cottage Pie

INGREDIENTS

4 lb

bone-in short ribs

1/4 cup

all-purpose flour

kosher salt and freshly-ground pepper

3 tbsp

vegetable oil

carrots ((about 1 cup), cut into 1/2-inch dice)

celery stalk ((scant 1/2 cup), thinly sliced)

medium onion (, cut in half and thinly sliced)

garlic cloves (, peeled and thinly sliced)

2 tbsp

tomato paste

1 tbsp

Worcestershire Sauce

3 cups

stout (*)

1/2 cup

low-sodium beef broth ((plus additional, if needed))

sprig rosemary

leaves from 5 small sprigs thyme (, stems discarded)

bay leaf

3 lb

Yukon gold potatoes (, peeled and cubed)

1/2 cup

milk or half and half

4 tbsp

unsalted butter (, melted)

1 3/4 cups

shredded Dubliner or sharp white cheddar cheese (, divided)

kosher salt (, to taste)

egg yolks

3/4 lb

cippolini or pearl onions (, peeled and halved if large)

3/4 lb

cremini or button mushrooms (, cleaned, trimmed, and quartered)

1 tbsp

vegetable oil

1 cup

frozen peas

1 tbsp

cornstarch, arrowroot powder, or tapioca starch (, dissolved in 1-2 tablespoons cool water; (a "slurry"))

1 tsp

chopped thyme leaves