Generously spray a 9 x 13-inch glass pan or metal sheet pan with high sides with cooking spray. Arrange 6 thick slices of babka in one layer on the prepared pan; set aside.
In a medium bowl with a lid or spout, whisk together 1 cup heavy cream, 1 cup whole milk, 3 tablespoons sweetened condensed milk, 3 large eggs, 1 teaspoon pure vanilla extract, 1 teaspoon ground cinnamon, and a pinch of kosher salt. Pour evenly over the arranged babka in the sheet pan. At this point, don’t worry if it seems like there’s too much liquid in the pan — the babka will absorb most of it! Cover with plastic wrap and refrigerate for at least 6 hours, preferably overnight.
When you’re ready to bake, center a rack in the oven and preheat to 350 (F).
Sprinkle 2 tablespoons demarara sugar and 1 tablespoon unsalted butter pieces over the bread. Cover the pan with aluminum foil, tenting it a little so that it doesn’t touch the surface of the babka. Use the tip of a sharp knife to poke several holes in the foil so that steam can escape.
Transfer to the preheated oven and bake until warmed through (a knife inserted into the center should feel warm to the touch), about 25 to 30 minutes. Remove foil and bake until deeply browned, 35 to 40 minutes longer. The babka should be crisp and golden; transfer to a wire rack to cool slightly, garnish with confectioner’s sugar and fresh fruit, and serve immediately. Enjoy!