Is there a combination of ingredients that will chemically interact to create poison? I am interested in whether this possible with any common preparation method (e.g. via cooking, blending, whisking, microwaving) but not by burning the food or leaving the food out to be contaminated by bacteria. I am interested in any ingredients that on their own are approved by some country's government as safe.
Basically everything at all normal is safe.
There is a mushroom that gets toxic if combined with alcohol, but alcohol itself isn't 100% safe and if you're gathering wild mushrooms you need to be safety conscious, so it's not really something you could run into by accident or with storebought ingredients.
Relevant paragraph from Wikipedia
Consuming Coprinopsis atramentaria within a few hours of alcohol results in a "disulfiram syndrome". This interaction has only been known since the early part of the twentieth century. Symptoms include facial reddening, nausea, vomiting, malaise, agitation, palpitations and tingling in limbs, and arise five to ten minutes after consumption of alcohol. If no more alcohol is consumed, they will generally subside over two or three hours. Symptom severity is proportional to the amount of alcohol consumed, becoming evident when blood alcohol concentration reaches 5 mg/dL, and prominent at concentrations of 50–100 mg/dL. Disulfiram has, however, been known to cause myocardial infarction (heart attack). The symptoms can occur if even a small amount of alcohol is consumed up to three days after eating the mushrooms, although they are milder as more time passes. Rarely, a cardiac arrhythmia, such as atrial fibrillation on top of supraventricular tachycardia, may develop.