Biscuit Topped Chicken Pot Pie

Chicken Mixture:

In large saucepan, heat oil over medium-high heat; saute carrots, mushrooms, onions, tarragon, salt & pepper until onion is softened - about 8 minutes.
Add flour; cook, stirring, for 1 minute.
Gradually whisk in milk & stock; bring to a boil, stirring.
Add beans.
Reduce heat & simmer, stirring often, until thick enough to coat back of spoon, about 6 minutes.
Stir in chicken and mustard.
Spoon into round 8-cup (2L) baking dish; set aside.

(Make-ahead directions: Let cool for 30minutes, refrigerate, uncovered, until cold. Cover & refrigerate for up to 2 days, rewarm in microwave to continue).

Biscuit Topping:

In food processor, pulse together flour, baking powder and salt; pulse in butter until crumbly.
Drizzle in milk, pulsing just until soft sticky dough forms.
Turn out onto floured surface; knead 10 times or until smooth.
Pat out to fit top of baking dish.
Cut into 8 wedges; arrange over chicken mixture.
Bake on rimmed baking sheet in 400F (200C) oven until biscuits are golden and no longer doughy on bottom, about 40 minutes.