Step 1: Slice the heirloom tomato into thick rounds, approximately 1/2 inch thick.
Step 2: Place the tomato slices on a paper towel and sprinkle both sides with flaky sea salt. Let sit for 5 minutes to draw out excess moisture.
Step 3: Spread a generous tablespoon of mayonnaise onto each slice of bread, ensuring the edges are covered to create a moisture barrier.
Step 4: Arrange the seasoned tomato slices on one piece of bread, overlapping them slightly for full coverage.
Step 5: Sprinkle with freshly cracked black pepper and add basil leaves if using.
Step 6: Place the second slice of bread on top and press down gently. Let the sandwich sit for 1 minute before slicing and serving.