I like to start by cutting the bread slices in half for more manageable pieces of French toast. You can skip this step if you prefer.
In a shallow baking dish or a medium mixing bowl, beat the eggs with a fork.
Add the milk, maple syrup, vanilla, cinnamon, cardamom, nutmeg, and salt, and mix well.
Set a frying pan over medium heat or set an electric skillet in the medium range. Throughout cooking, you may need to toggle between medium and medium-low to brown the French toast and cook it through in complementary timeframes.
Melt some of the butter on the pan or skillet, in proportion to the number of slices you'll be cooking at once.
Dip bread slices into the batter a few at a time, turning to coat well, and saturating them without letting them fall apart. Or, if you prefer, arrange the slices in a single layer on a rimmed half sheet pan and pour the batter overtop, flipping the bread at least once and ensuring each slice gets saturated. Either way, you should comfortably use all the batter to soak all the bread. (If soaking on a baking sheet, you can do this step before firing up the skillet.)
Cook in batches, flipping once, until lightly browned and cooked through, and adjusting the heat as necessary.