The surprising thing about Viña Mayu Pedro Ximenez is two-fold; first that it is an unfortified wine made with PX grapes and, second, which it is from Chile. Admittedly the former is less surprising than the latter.
Most (excepting the most cantankerous) will admit that Pedro Ximenez as a white varietal hasn't been all that common. This is changing. There are a number of PXs out there now in a wide range of prices.
This wine has a peppery (o maybe just "spicy" is the term to use) and mineral heavy taste. There is a medium amount of acid to add some pizazz here (to use a very technical wine term). You will see talk of the fruit flavors in the wine? Meh...if anything there is a floral sort of taste more than fruit. To me this wine is all about the spice and the minerals. This is a solid wine to serve cold on a hot day. As a vegetarian I would eat it with Mediterranean food--hummus, dolmas or any light food with some garlic involved.
Mayu Pedro Ximenez is grown at a fairly high elevation of over 6,000 feet. There is a great deal of evidence that growing SOME grapes at higher altitude changes the flavor of the grapes for the better--grapes grow thicker skins and flavors appear more concentrated. Most of what I have read on the subject has been about red grapes but it is hard to imagine that there is no change when it comes to white grapes. High altitude changes the amount of oxygen, UV exposure, temperature and other things I am likely forgetting that a plant needs to grow and thrive.
Some grapes won't grow at a high altitude of course which means the wine won't be very good because it does not actually exist.
The vines in the area are old vines--but were hitherto used to make Pisco, liquor that is Chile's pride and joy...and Peru's too. If you want to have some fun tell a Chilean Pisco is Peruvian (and visa versa).