Move rack to bottom position and preheat oven to 400 degrees.
In a large bowl, combine flour, sugar, baking soda, baking powder and salt.
Grate frozen butter and cut in with a pastry blender.
Put 1/2 Tbsp vinegar in a measuring cup and add milk until 1/2 cup. Stir and let rest for 5 minutes (this is making buttermilk). After 5 minutes, add another 1/2 cup milk.
Whisk together milk and egg.
Mash bananas.
Add milk & egg mixture and mashed bananas into the flour mixture, and combine with pastry blender.
Stir in diced strawberries with a fork until incorporated.
Using a cookie scoop, scoop mixture onto a parchment lined cookie sheet, positioning 1 inch apart.
Sprinkle each banana strawberry muffin top with a bit of sugar.
Bake until golden, about 12 to 14 minutes. Cool.
To make glaze, rapidly whisk together powdered sugar, butter, vanilla and milk. Allow to cool slightly, whisking periodically.
Using a whisk, drizzle glaze onto cooled scones.