... where he treated himself to filet mignon.

[constantinusphilo]

Dean Kountz, The Watchers:
Feeling like a million bucks, he returned to his van, drove home, showered, and went out to dinner at the nearest Stuart Anderson steak house, where he treated himself to filet mignon.

Why there is no article before 'filet mignon'?

 

[emsr2d2]

The writer is referring to it as a specific type of food, not the single dish that he ate. Here are a couple of other examples in which no article would be used:

I'm going to treat myself to pizza and beer tonight.
Shall we have steak or spaghetti carbonara for dinner?

 

[Rover_KE]

NOTE: AE filet mignon = BE fillet steak