Preheat the oven to 425F.
Dice potatoes.
Dice carrots and onions.
Heat a large pan over medium heat. Add the oil.
Saute potatoes until they are partially translucent.
Add carrots and onions and saute until soft. Do not allow them to brown.
Add butter and salt to the sauteed vegetables.
In a small bowl, stir broth and milk together.
Place flour into a large bowl. Whisk in ⅓ of the broth and milk until smooth. Add remaining broth and milk mixture.
Slowly add flour, broth, and milk mixture to the pan, stirring as you add it.
Once combined, add celery salt, thyme, peas, and green beans. Stir until combined.
Pour into an 8” pan or 8 x 8” casserole dish. Top with crust or biscuits.
If you’ve used crust, cut slits into the crust to vent it. Brush the tops of your crust of biscuits with milk.
Bake for 30 - 45 minutes, until the crust is golden brown.