In a large bowl, whisk eggs, milk, and salt. Add bread and briefly soak until coated, 1 to 2 minutes per side.
In a large nonstick skillet over medium heat, heat 1 Tbsp. butter. Working in batches, cook French toast, undisturbed, until custard firms up and turns golden on one side, 3 to 4 minutes. Flip and continue to cook until custard firms up on the other side, about 3 minutes more. Repeat with 1 Tbsp. butter and remaining French toast.
Meanwhile, in a large bowl, using a handheld mixer on medium-high speed, beat remaining 6 Tbsp. butter until light and fluffy, 1 to 2 minutes. Add raspberry preserves and cinnamon and beat until mixture is smooth and cohesive; it will be a deep pink.
Serve French toast with whipped raspberry butter and maple syrup alongside.
