Preheat a waffle iron and lightly grease. Into a large bowl, sift the dry ingredients together.
In a clean bowl, beat the eggs. Add the buttermilk, vanilla, and melted butter and beat to combine. Fold the wet ingredients into the dry ingredients. Let sit for a few minutes. (Batter can be made ahead, covered, and refrigerated for up to a week.) Lightly oil the sliced peaches and grill in a hot grill pan or outside on a grill until you get some nice grill marks. Pour the batter into the hot waffle iron and cook until golden brown and lightly crisp. Top waffle with grilled peaches, mascarpone, maple syrup or honey, and pecans.