Heat oven to 375°F. Grease and line two 7.75 × 3.75-inch loaf pans.
Whisk dry ingredients together.
Whisk wet ingredients together.
Add dry to wet; whisk just until combined.
Fold in sanding sugar.
Combine streusel ingredients (flour, sugar, salt, melted butter, vanilla). Keep at room temperature.
Divide batter between pans, filling each one ⅓ full.
Sprinkle a thick even layer of streusel; lightly press.
Add remaining batter and spread gently as a thin layer.
Finish with a very generous streusel layer. Do not press.
Sprinkle additional sanding sugar (optional).
Bake 40 minutes. Tent with foil if streusel browns too quickly.
Bake until a tester in the cake comes out with moist crumbs.
Cool 20 minutes in pans, then transfer to a rack.
Whisk glaze ingredients (powdered sugar, non-dairy milk, vanilla, salt).
Drizzle glaze over cooled loaves.
Chill for 30-40 minutes.
