Using a long serrated knife, trim crusts from bread, and cut each bread slice diagonally into 4 triangles. To prevent drying out, cover bread with damp paper towels, or place in a resealable plastic bag until ready to assemble sandwiches.
Spread a small amount of Horseradish Aïoli onto each bread triangle.
Fold each roast beef slice in half, then in half again to create a ruffled triangle. Place a roast beef triangle on aïoli side of 12 bread triangles. Top each with a tomato slice and another bread triangle, aïoli side down.
Garnish with microgreens, if desired.
Recipe by TeaTime Magazine at https://teatimemagazine.com/2-roast-beef-tea-sandwiches-recipe/