Slow-Cooker Steak & Guinness Pie

flour, plus more for rolling

Kosher salt and freshly ground black pepper

boneless beef chuck, trimmed of excess fat and cut into 1-inch cubes

large carrots, cut into 1/4-inch thick rounds

large yellow onion, chopped

large russet potatoes (about 1 1/2 pounds), peeled and cut into 1-inch cubes

large cloves garlic, minced

sprigs fresh thyme

bottle Guinness (or other stout)

low-sodium beef broth

sheet frozen puff pastry, thawed overnight in refrigerator