Preheat electric griddle to 350ºF (if using), or heat a stovetop griddle or skillet over medium heat.
Strawberry Syrup
To a small saucepan over medium heat, add the sugar and water, and stir to combine. Bring to a boil on medium heat, stirring frequently (3-5 minutes). Add sliced strawberries to the pan and simmer for about 5 minutes, until the mixture thickens. Meanwhile, start preparing the French toast.
French Toast
In a shallow container like a pie plate or dipping tray, whisk to combine the sugar, eggs, milk, and vanilla extract.
Melt butter in the preheated electric skillet or pan over medium heat.
Dip each side of the bread in the egg mixture (I let it sit for 15 seconds or so) then place it on the preheated griddle or skillet without crowding. Cook French toast slices until one side is golden brown, then flip to cook the other side. See Notes below to keep French toast warm until serving.
Just before serving, drizzle slices with strawberry syrup and whipped topping (if using).
Notes
How to dry bread for the best French toast: Place your bread on a cooking rack or baking sheet uncovered for 2 hours. How to keep your French Toast warm: Set your oven to 175ºF. Put an oven-safe plate, casserole, or baking sheet in the oven to preheat. Add your French toast to the oven as soon as it is cooked and keep it in there until you're ready to serve it. I cover it with damp paper towels or a clean tea towel to keep the sourdough French toast from drying out.