When he [Beethoven] came to Vienna, he knew nothing at all of the fine art of cooking.  He cared little about good food, his favorite dish being a mess of macaroni with plenty of cheese on top.  He liked, too, the simplest kind of stew, and fish from the Danube.  Ignaz Seyfried reported that Beethoven liked a kind of bread soup cooked like mush,

to which he looked forward with pleasure every Thursday.  Together with it, ten sizable eggs had to be presented to him on a plate.  Before they were stirred into the soup, he first separated and tested them by holding them against the light, then decapitated them with his own hand and anxiously sniffed them to see whether they were fresh.  When fate decreed that some among them scented their straw, so to speak, the storm broke.  In a voice of thunder the housekeeper was cited to court. (1)

He kept stracchino (an Italian cheese) and Verona salami in his room.  He so often forgot about mealtime that he must have taken a bite when he got hungry.  But once he did see himself in the role of master chef, having become sufficiently impressed by the fuss the Viennese make about cooking; he invited his friends to a dinner he was to cook himself.  Seyfried remembers:
They found their host in a short evening jacket, a stately nightcap on his bristly stock of hair, and his loins girded with a blue kitchen apron, very busily engaged at the hearth.
 

After waiting patiently for an hour and a half, while the turbulent demands of their stomachs were with increasing difficulty assuaged by cordial dialogue, the dinner was finally served.  The soup recalled those charitable leavings distributed to beggars in the taverns; the beef was but half done and calculated to gratify only an ostrich; the vegetables floated in a mixture of water and grease; and the roast seemed to have been smoked in the chimney.  Nevertheless the giver of the feast did full justice to every dish.  And the applause which he anticipated put him in so rosy a humor that he called himself "Cook Mehlschöberl," after a character in the burlesque, "The Merry Nuptials," and tried by his own example and by extravagant praise of the dainties which still remained to animate his continent guests.  They, however, found it barely possible to choke down a few morsels, and stuck to good bread, fresh fruit, sweet pastry, and the unadulterated juice of the grape. (2)

Source: Marek, George (1969) Beethoven: Biography of Genius. London: William Kimber, p. 171-172.

(1) O. G. Sonneck (ed., Beethoven: Impressions of Contemporaries, 1926
(2) Ibid.