In a medium bowl, combine pastry flour and salt. Add cold, cubed butter and cut into the flour mixture using a pastry blender or two butter knives, until the butter is the size of small peas.
Add ice water a few tablespoons at a time until the dough comes together to form a shaggy ball. Shape into a flat disc, wrap in plastic, and refrigerate at least 1 hour.
To roll out the pie shell, remove and discard the plastic surrounding the pie dough. Dust the work surface and the top and bottom of the pie dough disc lightly with flour. Begin rolling the dough, rotating a quarter turn between rolls to keep the dough from sticking and to better keep a uniform circle shape, until the dough is an 11 - 12-inch round circle and about 1/8-inch thick.
Carefully transfer the dough to a standard 9-inch pie dish and press the dough into the bottom edge of the dish. Trim off excess dough, leaving a 1-inch overhand around the top of the dish. Fold the overhang under itself to create a thicker crust then crimp the crust all the way around the edge using your fingers or a fork.
Transfer the pie crust to the freezer for at least 30 minutes and preheat the oven to 350°F.
While the pie dough chills, prepare the muesli crumble. In the bowl of a mixer fitted with the paddle attachment or in a bowl by hand, combine the muesli, flour, brown sugar, cinnamon and salt.
Add the cold cubed butter and mix until a crumbly mixture forms. Set aside.
In a large bowl, whisk the eggs and sugar until light and fluffy. Fold in the yogurt and vanilla extract.
Sift the flour into the mixture and fold gently to incorporate. If lumps form, whisk briefly to break them up.
Remove the pie crust from the freezer and pour yogurt filling into the crust. Top evenly with the muesli crumble.
Bake until the center of the pie barely jiggles when gently shaken, about 50 - 55 minutes. Let cool at least 1 hour before slicing and serving.