Chullin 193:1

שאני חלב דמפעפע

It is different with fat for it spreads [throughout the flesh].

ובחלב אסור

Is it then forbidden in the case of fat?

והאמר רבה בר בר חנה

But Sur Rabbah B'Bar Hana has related a case which came before R'Johanan at the synagogue of Ma'on of a kid that was roasted with its fat, and on enquiring of R'Johanan he ruled that one may cut away [the meat] and eat it until one reaches the fat! - That was a lean kid.<span class="x" onmousemove="('comment',' And it had little fat; or the fat of a lean animal would not spread (Tosaf.) .');">¹</span>

עובדא הוה קמיה דר' יוחנן בכנישתא דמעון בגדי שצלאו בחלבו ואתו ושיילוה לרבי יוחנן ואמר

R'Huna B'Judah suggested that it was the case of a kidney roasted with its fat, and he [R'Johanan] declared it to be permitted.<span class="x" onmousemove="('comment',' For the forbidden fat of the kidney could not penetrate the kidney by reason of the strong membrane which separates them.');">²</span>

קולף ואוכל עד שמגיע לחלבו

Rabin son of R'Ada said: It was the case of a kilkith<span class="x" onmousemove="('comment',' A small fish that may not be eaten; probably the stickleback.');">³</span>

ההוא כחוש הוה

that was found in a pot of stew, and on enquiring of R'Johanan he ruled that a gentile cook should taste it.<span class="x" onmousemove="('comment',' To ascertain whether the flavour of the fish is discernible in the stew. The cook's opinion, even though he is a gentile, would be relied upon only so long as he is ignorant of the issue that is involved.');">⁴</span>

רב הונא בר יהודה אמר

Raba said: In the past the following was always a difficulty to me.

כוליא בחלבה הוה ושריא

It was taught: In a pot wherein meat had been cooked a person may not boil milk, and if he did boil [milk] therein, it depends whether the pot imparted a flavour [to the milk] or not.<span class="x" onmousemove="('comment',' V. supra p. 540, n. 4.');">⁵</span>

רבין בר רב אדא אמר

[In a pot wherein] terumah<span class="x" onmousemove="('comment',' V. Glos.');">⁶</span>

כילכית באילפס הוה ואתו שיילוה לרבי יוחנן ואמר להו

food [had been cooked] a person may not cook common food, and if he did cook [common food] therein, it depends whether the pot imparted a flavour [to the common food] or not.

ליטעמיה קפילא ארמאה

Now in the case of terumah it is clear, for a priest could taste the food;<span class="x" onmousemove="('comment',' For to a priest both terumah and common food are permitted. He therefore could taste the common food to ascertain whether it contains any flavour of the terumah food which had previously been cooked in this pot.');">⁷</span>

אמר רבא

but in the case of meat and milk who may taste it?<span class="x" onmousemove="('comment',' For if one actually imparts a flavour into the other then it is forbidden to everyone, even only to taste thereof.');">⁸</span>

מריש הוה קא קשיא לי הא דתניא קדרה שבשל בה בשר לא יבשל בה חלב ואם בשל בנותן טעם

But now that R'Johanan ruled that we can rely upon a gentile cook, in this case too we could rely upon a gentile cook.

תרומה לא יבשל בה חולין ואם בשל כנותן טעם

Raba also said, [In certain cases] the Rabbis ruled that the test whether or not it imparts a flavour applie and [in other cases] the Rabbis ruled that one may rely upon a [gentile] cook,

בשלמא תרומה טעים לה כהן אלא בשר בחלב מאן טעים ליה

השתא דאמר רבי יוחנן

סמכינן אקפילא ארמאה הכא נמי סמכינן אקפילא ארמאה

דאמר רבא

אמור רבנן בטעמא ואמור רבנן בקפילא