This "Restaurant Mutter Ernst" is near the Hilton, in walking distance.
The area near the Hilton has some nice restaurants, all at/near "Fressgasse" ("Eating Lane"), Grosse Bockenheimer Str.
One is "Leiter" and next to it "Gallo Nero"; no German food in both, but both very good (in-places). For a snack, Pleuger Deli is a very good place.