Rashi on Genesis
הברכה אחת HAST THOU BUT ONE BLESSING? The ה in הברכה is the interrogative prefix, as in (Num. XIII. 19, 20) “whether in camps (הבמחנים)”, “whether it is fat (השמנה)", and (2 Sam. III. 33) “Should Abner die (הכמות) as a churl dieth”?
Radak on Genesis
ויאמר...אחת, can you not even grant me a blessing concerning any aspect of life which you have not given him?