In a large mixing bowl, combine all-purpose flour, salt, and chopped thyme. Cut in cold butter until the mixture resembles coarse crumbs. Gradually add ice-cold water, mixing until a dough forms, then chill in the refrigerator for 30 minutes.

Heat a Dutch oven over medium heat and melt some butter. Add diced onion and minced garlic, sautéing until fragrant. Toss in thinly chopped carrots and diced russet potatoes, cooking for about 5-7 minutes until slightly softened. Stir in flour, then slowly add chicken stock and coconut cream, stirring until thick and creamy.

Season the filling with salt, black pepper, cayenne, mustard seed powder, and fresh thyme. Gently fold in the shredded rotisserie chicken and frozen green peas, then remove from heat to let cool slightly.

Preheat your oven to 400°F. Roll out one portion of the chilled dough to fit your greased baking dish, pour in the filling, and cover with a second dough layer, rolled out to the same size. Trim the edges, and cut decorative slits for steam release. Brush with the beaten egg.

Place the assembled pie in the preheated oven and bake for about 30 minutes or until the crust turns golden brown. Allow to cool for 10 minutes before slicing.