Cut each slice of bread twice diagonally to make 4 triangles (24 total). Set aside.
Step 2
Beat together milk, eggs, vanilla, and cinnamon in a shallow bowl until well combined.
Step 3
Heat butter over medium-high heat in a frying pan or skillet. Working in batches, dunk bread triangles in egg mixture, soaking both sides. Cook bread triangles in hot butter until golden brown, 2 to 3 minutes per side. Serve warm.