Halakhah for Chullin 215:20

To not eat meat with milk: To not eat meat with milk that has been cooked together, as it is stated (Exodus 34:26), "you shall not cook a kid in its mother’s milk." And this verse comes to forbid eating and deriving benefit (pleasure) from the meat with milk. And let it not be difficult to you - [that] if so, why is its prohibition not stated explicitly, as "you shall not eat," and [instead] expressed with an expression of cooking. As the answer to this [is] because there is a novelty in the prohibition of its eating above the eating of the other prohibitions. As with other prohibitions, the liability is only if he enjoys his eating. But here even if he does not enjoy his eating, once he swallows it - and even if he swallows it hot and he burns his throat with it, and similar to it - he is lashed nonetheless. [It is] as they, may their memory be blessed, said in Pesachim 25a, "For this reason did [the Torah] not write, 'eating' in [the verse] itself: To say that one is lashed [even when consumed] not in the way of its enjoyment." And nonetheless, we do not administer lashes for it unless it is by way of cooking (Chullin 108a), according to the language that the verse expressed its prohibition.

And they were also stringent in this matter according to some of the commentators to [deduce] a novel prohibition in this, more than in other prohibitions of food (Chullin 108a). [It is] in that with the matter of meat with milk, if milk is mixed with meat, and there is not sixty parts in the piece of meat corresponding to the milk, we see both of them as one piece of prohibited food. And if this piece fell into a stew of meat or a stew of milk, we measure against all of [the piece]. And this is what, they, may their memory be blessed, said (Chullin 108a) "The piece itself becomes a carcass." And the reason is because their mixture is what makes them prohibited. And hence, after they have mixed, behold, they are like a piece of carcass. And with other prohibitions, it is not such; as [with] prohibited food that is mixed with a piece of permissible food and there is not sixty parts in the permissible food to negate the prohibited food, and afterwards they fall into a stew, we only measure according to the measurement of the prohibited food that fell into it, and [the permissible portion of the piece] itself helps to [count against] the prohibited food. [This is] because that piece does not become a carcass, and [so] the permissible food in it is found to be like the rest of the permissible food in the stew - and [so] it assists [in counting against] the prohibited food. However if it is recognizable, the piece itself is forbidden forever, according to the opinion of some of the commentators.