Preheat oven to 375°F with a rack in the center. Lightly oil a medium baking dish. Cut 2 mini baguettes into 1-inch pieces. Spread out on a rimmed baking sheet and toast on center oven rack until bread cubes are lightly browned, stirring halfway through, about 15 minutes.

Meanwhile, trim 2 scallions, then thinly slice, keeping dark greens separate.

In a very large bowl, whisk to combine 4 large eggs, 1¾ cups water, and ½ teaspoon each of kosher salt & ground pepper. Add all of the 2 (3 oz) mascarpone and gently whisk to combine.

Heat 1 tablespoon olive oil in a medium nonstick skillet over medium-high. Add ½ lb pkg country-style sausage and cook, breaking up into smaller pieces, until browned, about 6 minutes. Stir in scallion whites and light greens and cook until softened, about 2 minutes.

To custard in large bowl, add toasted bread, sausage mixture, dark green scallions, and 1⅔ cups of the 2 (2 oz) shredded fontina (save rest for next step). Gently fold to combine and to evenly moisten bread cubes.

Scrape mixture into prepared baking dish and spread to an even layer. Cover with lightly oiled foil and bake on center oven rack, 20 minutes. Uncover, then top with remaining cheese, and return to center oven rack to bake until top is golden brown, about 20 minutes. Let rest for 10 minutes before serving. Enjoy!