Green’s Dictionary of Slang

a small portion, a dab, pat or dollop.

1953		T.A.G. Hungerford Riverslake 56: Like a dob of wet clay.
1969		L. Hadow Full Cycle 233: Cabbage, a sodden grey dob.
1976		D. Ireland Glass Canoe (1982) 139: Gravy and chops, and dobs of mashed potato and squashy pumpkin.
1980		M. Bail Homesickness (1999) 201: A mother [...] dropped dobs of Wam into her son’s stained mouth.
1991		M.B. ‘Chopper’ Read Chopper From The Inside 69: I would leave dobs of jam under their beds to attract ants.
1999		Indep. Rev. 25 Sept. 20: How much butter?, I asked. ‘Oh, a decent dob,’ came the reply.