
Heat the oil and butter in a pot over low heat.
Add the onion; cook,
stirring, for 10 minutes. Add the garlic; cook
2 minutes more.
Sprinkle with the flour and tarragon; cook, stirring
constantly, for
1 to 2 minutes more.
Add the carrots, potatoes, apple, and broth; bring
to a boil. Reduce
heat to a gentle simmer and cook, partially covered,
until the
vegetables are tender, about 20 minutes. Add the
peas, dill, tomato,
and chicken; season to taste with salt and pepper,
then cook 5
minutes more.
Preheat the oven to 350F. Spoon the mixture into
a 2-quart round
ovenproof casserole. On a lightly floured surface,
roll puff pastry
out to form a circle 2 inches larger than the casserole.
Brush some
egg wash around the inside and outside rim of the
casserole. Lay the
pastry over the top, trim the overhang to 1 inch,
and crimp the edges
around the rim to seal. Cut several slits in the
pastry to release
the steam, then brush with remaining egg wash.
Bake until crust is
golden, 40 to 45 minutes.
