Classic Tomato Sandwich with Homemade Mayonnaise

‍For the homemade mayonnaise:

1. Add egg, salt, dry mustard, paprika, lemon juice, vinegar, and garlic (if using) to a food processor. Pulse a few times to combine.
2. Measure the oil into a vessel with a spout (measuring cup with a pour spout works well).
3. With the processor running continuously, add the oil in a very thin, slow, steady stream through the feed tube — the slower the better for the first ¼ cup especially, since that's when it emulsifies. Adding it too fast is the #1 reason mayo breaks.
4. Keep streaming until all the oil is incorporated and the mixture is thick, pale, and holds its shape. Taste and adjust salt or lemon juice if needed.
5. Transfer to a jar and refrigerate. Keeps about 1 week.

For the sandwich:

1. Salt and pepper the tomato slices. Lightly toast the bread.
2. Spread a generous amount of mayonnaise on each slice of bread. Divide the tomato slices between 2 slices of bread, add torn basil leaves, and then sandwich with the remaining bread.
3. Cut the sandwiches diagonally, and serve/eat immediately.