Preheat the oven to 350 degrees F.
Combine the flour, sugar
in a small bowl. Add 8 tablespoons of the melted butter and combine until crumbly. Refrigerate for 15 minutes.
Slice a very thin piece off the bottom of each peach half so they have flat bottoms. Brush the bottom and sides of a 9- by 11-inch baking dish
with some of the remaining 3 tablespoons of melted butter, and then brush the rest of the butter on the peaches. Place the peaches in the pan cut-side up and about an inch or so apart. Sprinkle a little bit of salt on the peaches. Top each peach with some of the streusel. Bake in the oven until the peaches
are soft and the streusel
is lightly golden brown, 45 to 55 minutes, depending on how ripe the peaches are.
When the peaches are almost done, put the syrup in a small saucepan
and bring to a simmer
on low heat, Keep warm. Serve the peaches drizzled with some of the syrup and topped with whipped cream
, if using.