The machine that makes the machines.
Today, the WSJ calls it the "Most Indispensable Machine in the World" as ASML alone makes the only machine that can manufacture advanced chips for Apple, NVIDIA, etc.

It costs $370 million and needs three 747s to transport. It comes with a dedicated engineer to keep it running. To make the short wavelength EUV light, twin lasers (which need ultra-pure diamond windows) blast suspended tin droplets 50,000 times per second, heating them up to be hotter than the sun. The plasma emits light that follows the purple path bouncing off multi-layer curved mirrors, the smoothest object ever manufactured (as lenses would not work with this light). Each machine had 457,329 parts and took 20 years to develop, the advanced alchemy of computation.

But, as the diagram shoes, to continue shrinking feature sizes on our chips, shorter wavelengths of light inevitably carry more energy per photon, and this is proving to be a problem for continued scaling using light (damaging the photoresist on the wafers and blurring the results).

From my book review on its history, below: “EUV was one of the biggest technological gambles of our time. Intel alone invested $4B in ASML in 2012, an investment that followed billions of dollars of previous grants and investments Intel had spent on EUV, dating back to the era of Andy Grove.”

"ASML’s EUV lithography tool is the most expensive mass-produced machine tool in history"

And the concentration extends to TSMC: "Today, Apple’s most advanced processors can only be produced by a single company in a single building, the most expensive factory in human history.”