**Core Concept**
The patient's symptoms are characteristic of an allergic reaction, specifically a type of hypersensitivity reaction known as immediate hypersensitivity, also known as anaphylactic or IgE-mediated hypersensitivity. This reaction involves the release of histamine and other mediators from mast cells and basophils in response to an allergen.

**Why the Correct Answer is Right**
The patient's symptoms are caused by the release of histamine and other mediators from mast cells and basophils. The allergen, in this case, is the nut protein. When the patient eats the cookies, the allergen binds to specific IgE antibodies on the surface of mast cells and basophils, leading to the activation of these cells and the release of histamine and other mediators. Histamine causes blood vessels to dilate, leading to increased blood flow and permeability, resulting in the characteristic symptoms of an allergic reaction, including blotchy, erythematous, slightly edematous, pruritic plaques.

**Why Each Wrong Option is Incorrect**
* **Option A:** T cells are not directly involved in the immediate hypersensitivity reaction and do not release histamine or other mediators.
* **Option B:** Neutrophils are not typically involved in the immediate hypersensitivity reaction and do not release histamine or other mediators.
* **Option D:** Platelets are involved in blood clotting and are not directly involved in the immediate hypersensitivity reaction.

**Clinical Pearl / High-Yield Fact**
Mast cells and basophils play a crucial role in the immediate hypersensitivity reaction, and the release of histamine and other mediators from these cells is responsible for the characteristic symptoms of an allergic reaction. This reaction can range from mild symptoms such as hives and itching to life-threatening anaphylaxis.

**Correct Answer:** C.