"a small, light, round, spongy cake made with eggs," usually eaten buttered and toasted, 1703, moofin, possibly from Low German muffen, plural of muffe "small cake;" or somehow connected with Old French moflet "soft, tender" (said of bread). The historical distinction of the muffin from the crumpet is not entirely clear and the subject is involved. In American English the word was extended to a sort of cup-shaped bun or cake (often with blueberries, chocolate chips, etc.); hence muffin top "waistline bulge over tight, low jeans" (by 2005), from resemblance to baked muffins from a tin. Muffin-man "street seller of muffins" is attested by 1754.
Why sit we mute, while early Traders throng
To hail the Morning with the Voice of Song?
Why sit we sad, when Lamps so fast decline,
And, but for Fog and Smoke, the Sun would shine?
Hark! the shrill Muffin-Man his Carol plies,
And Milk's melodious Treble rends the Skies,
Spar'd from the Synagogue, the Cloathsman's Throat,
At measur'd Pause, attempers every Note,
And Chairs-to-mend! with all is heard to join
Its long majestic Trill, and Harmony divine.
["The Black Bird and the Bull-Finch," 1777]