Combine milk, cocoa powder, sugar, vanilla, and salt in a mixing bowl, whisking until the cocoa and sugar are fully dissolved and the mixture is smooth.
Pour the custard mixture into a shallow dish, ensuring it covers the bottom evenly for easy dipping.
Dip each bread slice into the custard, allowing it to soak for about 30 seconds, flipping to ensure an even coating. The bread should be well-absorbed but not falling apart.
Heat a skillet or non-stick pan over medium heat and add 1 tablespoon of butter. Once melted and bubbly, place the soaked bread slices into the pan.
Cook the bread for 2-3 minutes on each side until golden brown and crispy edges develop, producing a slight sizzling sound. Use a spatula to turn the slices, and check for even browning.
Remove the cooked French toast from the pan and serve immediately. Optional toppings include powdered sugar, syrup, or fresh berries.
