For the dough: Whisk together the bread flour, mashed potato flakes, granulated sugar, cinnamon, yeast and salt in a large bowl. In the bowl of a stand mixer fitted with the dough hook, add the milk, vanilla and eggs; whisk to break up the eggs. Add the dry ingredients to the wet ingredients and mix until the dough just comes together.
Add the butter, one piece at a time, mixing until incorporated. Continue to mix until the dough comes together in a ball. If the dough is sticking a lot to the sides of the bowl, add a little more flour, 1 tablespoon at a time, until most of the dough no longer sticks. (A little sticking to the bottom of the bowl, beneath the hook, is fine. Adding too much flour will make the buns dry, so use a light hand.)
Transfer the dough to a lightly floured work surface and knead by hand until shiny and smooth, 5 to 10 minutes. (The dough should be very soft but not wet and sticky; a little tacky is OK.) Place the dough in a large bowl sprayed with nonstick spray; lightly spray the top of the dough. Cover with plastic wrap and let rise in a warm corner of your kitchen until doubled in size, 45 to 60 minutes.
For the filling: Stir together the granulated sugar and cinnamon in a small bowl.
Roll the dough out into a long rectangle, about 10-by-21 inches. Brush with the melted butter, then sprinkle with the cinnamon sugar, followed by 4 cups of frozen Crumble. Starting from a long side, roll the dough into a jelly roll.
Cut the log into 2-inch pieces and place, cut-side down, in a buttered 10-inch square baking pan. Sprinkle 1 cup of Crumble over the top. Cover with plastic wrap and let rise until puffy and nearly doubled in volume, 30 to 45 minutes
Preheat the oven to 350 degrees F. Bake the buns, loosely wrapped in foil, for 15 minutes. Remove the foil and bake until golden brown on top, about 5 more minutes.
For the glaze: Meanwhile, combine the confectioners' sugar, milk and vanilla in a small bowl and stir until smooth.
While the buns are still warm (but not hot), drizzle with the glaze. Serve warm.
Combine the all-purpose flour, melted butter, brown sugar, granulated sugar and salt in a large bowl. Stir together and then work with a spoon or your fingers until the butter is absorbed and the mixture forms clumps. Place in a resealable plastic bag and freeze until needed.
If you don't want to bake the cinnamon buns the same day, wrap the pan completely in plastic wrap and then foil, and freeze for up to 2 months. Defrost in the refrigerator for a few hours or overnight before baking (be sure to remove the plastic wrap first!). The Crumble can also be used as a blueberry muffin topper or turned into a quick fruit crisp. For the crisp, toss fresh fruit, such as blackberries, with a bit of cornstarch and some brown sugar, then place in ramekins and top with Crumble before baking.