The most important thing is to get the timing right. Fill a pot with water and put the eggs in. The size of your pot probably matters. Mine is 3 quarts, 7 inches wide, made in Clinton, Illinois, USA. It was a gift to my parents when they got married. It's the pot you don't watch when you're boiling water. Except when you're making egg on toast, because you put the eggs in the pot with the water cold.
I turn the burner on medium-high. It's better if you have a gas stove. On an electric stove, the eggs will cook on the side that's touching the burner before they can be properly soft-boiled. This defeats the purpose of boiling them.
In the French tradition of mise-en-place, this is when I put two slices of bread in the toaster and get the butter out of the refrigerator. It's hard to time the toast with the eggs. The trick is to have hot, just-popped and buttered toast without over-cooking the eggs.
When the water is just about to boil, but not quite, this is when you put push the bread down to make toast.
This is one place where my mom and I diverge in how we make egg on toast. She suggests setting a timer for three minutes just before the water starts to boil. I wait until the water comes to a rolling boil, and then I turn the burner down to medium-low and set the timer for two minutes.
This is where things can go off the rails with the toast. If two minutes passes and your toast isn't done and buttered, you're at risk of over-cooking the eggs.
Let's say everything is going according to plan. Your toast is done on time. Butter it, and put the two slices side by side on a plate.
I use 7.5-inch salad plates made in Japan. They belonged to my mom's parents before they somehow became mine. I'm not sure how they became mine, or really what my grandparents served on them. Maybe they were the original canvases to Lee Luskey's Caesar Salad?
I remember using these dishes in Seattle, serving egg on toast on them in my senior year of college.
A few years ago, I bought some white dishes from Fishs Eddy that are 9 inches. I invested in these dishes because they fit in the standard 12-inch cabinets that had shelves that were only 10-inches wide. I needed real dinner plates--I was facing a lifetime of eating every evening meal off of a salad plate and I wasn't satisfied with that prospect. I found it difficult to find respectable dinner plates that were smaller than 13 inches. The white ones from Fishs Eddy are Syracuse china, labeled USA. As far as china goes, they are heavy. They are restaurant-style dishes that can take a beating but burn out in the microwave.
When the egg timer goes off, lift the first egg out of the boiling water and run it under a cold stream of water from the tap.
In New York, I don't worry about how long I leave the tap running. The sound of flowing water left on in an absent-minded moment feels luxurious, like pouring champagne into a hot tub. In the summer, I let the water run for a minute to get as cold as it will come, and sometimes it comes out so chilled it almost feels like it's already been refrigerated.
Let the egg cool just enough to stop cooking, so you can hold it without burning yourself. Then, take a sharp table knife and slice it through the middle of the egg. My mom is really good at that part--cracking open the egg without getting shards of shell all over. Sometimes I get it right, and sometimes I don't. When I get it wrong, I blame it on the knife. Too dull. Serrated edges too wide. Handle versus blade weight is off balance. But you do the best you can with what you have. I'm pretty good at picking shell out of my egg.
Repeat with the next egg. Work as quickly as possible; the eggs keep cooking before they are cracked open.
Once the egg is on the toast, plated, you can stack the pieces of toast and cut them into bite-sized pieces. It tastes better when served that way.