Мидраш к Вайикра 2:4

1) (Vayikra 2:4): "And if you bring (an offering of a meal-offering, etc."): "if you bring" — it is optional (not mandatory). "an offer (korban) of a meal-offering": R. Yehudah said: Whence is it derived that if one says: "I take upon myself a baked meal-offering" that he may not bring part cakes and part wafers? From "an offer" — he brings on offering, and not cakes and wafers.

1) (Vayikra 7:9) ("And every meal-offering that is baked in the oven, and all that is made in the stewing-pan and on the griddle, to the Cohein who offers it up, to him shall it be. (Vayikra 7:10) And every meal-offering mixed with oil or dry, to all the sons of Aaron shall it be, one man as well as another.") R. Yossi b. R. Yehudah said: Whence is it derived that if one said: "I vow (to bring) a burnt-offering of meal baked in an oven" that he should not bring half-cakes (challoth) and half-wafers (rekikim)? From "every meal-offering that is baked in the oven, and all that is made in the stewing-pan and on the griddle … and every meal-offering mixed with oil or dry." Just as the latter ("stewing-pan and griddle" and "mixed with oil or dry") are (respectively) two kinds, so, these ("cakes and wafers" — viz. Vayikra 2:4 ("baked in an oven…) cakes and wafers") are two kinds (and cannot combine with each other to constitute a vow connoting a single kind). "and all that is made in the marchesheth (stewing-pan) and the machavath (griddle)." These terms connote the vessels (themselves) and not their products. Just as a tanur ("oven") is a vessel, so marchesheth and machavath are vessels.

2) "soleth mixed (with oil"): We are hereby taught that it is mixed (with oil) while it is soleth. Rebbi says: It is (thus) mixed (when they are at the stage of) challoth, viz. (Vayikra 2:4): "challoth … mixed" — whereupon they said to him: Are not "challoth" mentioned in respect to the thanksgiving loaves (Vayikra 7:12), and it is impossible to mix them (with oil) when they are challoth, (there being too little oil for that); but (it must be that the oil is mixed with) soleth. How is this done? He places oil in the vessel before processing (the meal-offering). Then he places oil on it (the soleth), and mixes it, and kneads it, and breaks it into pieces, and pours oil on it, and takes the fistful. Rebbi says: He mixes them (with oil) when they are challoth, viz.: "challoth … mixed with oil." How is this done? He places oil in the vessel before processing it, and places (oil) on it, and kneads it, and bakes it, and crumbles it, and places oil on it, and mixes it, and then again pours oil on it, and takes the fistful. "unleavened": I might think that this is a mitzvah specification only; it is, therefore, written "shall it be" — Scripture makes it a categorical requirement.