For the pie crust crackers:

1. After cubing the butter, put it in the freezer for 20 minutes to chill.
2. Meanwhile, in a food processor, pulse the flour and the salt until incorporated. Add the chilled butter pieces and pulse until butter pieces are the size of small peas (about 20 pulses). Then add ice water and pulse until the dough starts to stick together (about 20 pulses)
3. If you don't have a food processor, mix the flour and the salt in a large mixing bowl until incorporated. Add the chilled butter pieces and using a pastry blender (or your hands), cut the butter and the flour until small pea-sized butter pieces remain. Then add ice water and mix until the dough just sticks together when you squeeze it.
4. Dust a clean countertop with flour and turn the dough out of the food processor or bowl onto your workspace. Separate the dough into two equal discs and wrap in plastic wrap. Place one of the discs in the freezer for another use, and chill the other dough in the refrigerator for 30 minutes (up to two days).
5. Preheat oven to 375°F.
6. Place the chilled dough on a piece of floured parchment paper
7. Roll the dough into a 12-inch rectangle and poke it all over with the tines of a fork. Score the dough lightly with a knife into cracker-sized pieces (this will make it easier to cut apart later).
8. Transfer the dough on the parchment paper to a baking sheet and bake until golden brown, about 30 minutes.
9. Cool the pie crust and using a knife, cut along the score lines into crackers.

For the soup:

1. Poach the chicken breasts in water for 15 minutes; remove, dice into bite-sized cubes and set aside.
2. In a saucepan, bring the broth and the milk to a simmer, and keep at a simmer.
3. In a soup pot, heat the butter over medium-high heat until foamy. Add the minced garlic and sauté, stirring until fragrant, about 1 minute).
4. Add the flour and reduce heat to medium, stirring constantly until mixture is a toasted color and foaming, about 3 minutes. Slowly whisk in the broth-milk mixture. Add salt and pepper, bring to a boil, then reduce heat and cook until mixture has thickened, about 5 minutes.
5. Add the potato, carrots, peas, pearl onions, apple, celery and mushrooms, and simmer until potatoes are tender, about 20 minutes.
6. Stir in chicken, heavy cream and thyme and heat for another 5 minutes. Season with salt and pepper to taste and serve with pie crust crackers.