Using a 2-inch square cutter, cut out 2 pieces from each slice of bread.
Using a mandoline, slice tomatoes into ⅛-inch-thick slices. Using a 1-inch round cutter, cut 2 circles from each slice of mozzarella. Slice each 1-inch circle in half to make 2 (⅛-inch thick) circles.
Shingle tomatoes and mozzarella on each slice. Drizzle with balsamic glaze and extra-virgin olive oil. Sprinkle with flaky sea salt; garnish with basil and cracked pepper, if desired.
Recipe by Victoria at https://victoriamag.com/open-faced-caprese-tea-sandwiches/