Preheat the oven to 425 F and heat 2 tsp oil in a large skillet over medium heat.

Add leeks and carrots.

Cook while stirring until leeks soften and become fragrant. About 6-8 minutes.

Add garlic and continue to cook while stirring for 1 more minute.

Pour in wine and stir until most liquid has evaporated.

Add flour and sage and continue to cook while stirring. The flour should start to turn a light brown. About 2-3 minutes.

Stir in broth and simmer.

Stir constantly and wait until sauce thickens and carrots are just tender. About 4-6 minutes.

Add chicken and peas.

Season to taste with salt and pepper.

Transfer everything to a deep 10 inch pie pan and set aside.

Place potatoes in a large pot and add cold salted water to cover them.

Bring to a boil over medium heat.

Cook partially covered until potatoes are tender 10-12 minutes.

Drain water and keep potatoes in pan.

Remove from heat and allow potatoes to dry a bit.

Mash potatoes and add buttermilk to make a smooth puree.

Season with salt and pepper.

Stir in egg and olive oil.

Spread potatoes on chicken mixture.

Set dish on a baking sheet and bake until potatoes and filling are heated through. Top will turn golden brown about 25-35 minutes.