If using fresh bread, adjust oven rack to middle position and preheat oven to 225°F (110°C). Set a wire rack in a rimmed baking sheet. Using a bread knife, remove crusts from bread, then cut into four rectangular pieces that are 2 inches thick and about 1 ½ inches wide and 4 inches long. Arrange bread pieces on prepared baking sheet, leaving at least 1 inch of space between each piece, and bake, flipping pieces over halfway through, until lightly toasted and dry on their surface, 30 to 45 minutes. Transfer baking sheet to a heatproof surface to cool slightly, and increase oven temperature to 375°F (190°C). If using stale bread, you can skip the toasting step; cut the bread into pieces as described and preheat oven to 375°F.

Meanwhile, in a 2-quart saucier or saucepan, combine milk, cinnamon, vanilla, orange zest, and salt. Set over medium-low heat and cook, stirring frequently with a rubber spatula, until milk registers 190°F (88°C) on an instant-read thermometer, 3 to 5 minutes. Remove from heat, cover, and set aside to steep for 30 minutes.

While the milk steeps, whisk together ¼ cup (50g) sugar and egg yolks in a medium bowl until sugar is dissolved and mixture turns pale yellow, 2 to 3 minutes. Set a fine-mesh strainer over bowl with egg mixture, and slowly pour one-third of milk mixture into yolk mixture to temper, whisking constantly to prevent yolks from curdling. Add remaining milk mixture, whisking constantly until well-combined; set aside but don't clean strainer; wipe out saucepan.

Add bread to custard base and soak, turning pieces occasionally to ensure they are coated on all sides, until fully saturated and soft, 5 to 6 minutes. Using a small spatula, carefully transfer bread pieces to a plate, allowing excess liquid to drip back into the bowl of custard base; set bread pieces aside.

Strain custard base through fine-mesh strainer into now-empty saucier; you should have between ¾ to 1 cup (175 to 240ml) of liquid. Return to stovetop; once again set aside but don't clean strainer, and wipe out bowl. Cook over medium-low heat, stirring constantly with a rubber spatula or wooden spoon to prevent egg yolks from curdling, until mixture registers 175°F (79.5°C) on an instant-read thermometer and thickens slightly so that it coats the back of a spoon, 3 to 5 minutes. Working quickly, remove from heat and pour crème anglaise through fine-mesh strainer back into now-empty bowl. Place piece of plastic wrap directly on surface of crème anglaise to prevent skin from forming, and refrigerate until ready to use.

In a medium cast iron skillet, melt butter over medium-high heat until just foaming. Sprinkle 2 tablespoons (25g) sugar in an even layer over butter, then add bread pieces to skillet. Cook, carefully turning pieces occasionally, until lightly browned on all sides, 4 to 5 minutes. Transfer skillet to oven, and bake until bread pieces are heated through at the center, about 5 minutes.

Remove skillet from oven, and carefully flip bread pieces over so that bottom sides that were in contact with the pan are facing up. Sprinkle remaining 1 tablespoon (13g) sugar evenly over bread pieces. If using a blowtorch, ignite torch and caramelize sugar by sweeping flame 2 inches above bread pieces, until sugar is bubbling and deep golden brown. If not using a blowtorch, simply serve with the sprinkled sugar on top.

Divide crème anglaise between individual serving plates, followed by bread pieces. Serve immediately.