Pain Perdu (Classic French Toast)

Ingredients

• ¾ cup plus 1 Tbsp. heavy cream
• 1 cup (200 g) granulated sugar
• 6 Tbsp. unsalted butter, cut into small pieces
• Fleur de sel or kosher salt
• 1¼ cups chilled heavy cream
• ¼ cup mascarpone
• ¼ cup (28 g) powdered sugar
• ½ vanilla bean, split lengthwise, or 2 tsp. (or more) vanilla bean paste or vanilla extract
• 4 large eggs
• ⅓ cup (67 g) granulated sugar
• ½ vanilla bean, split lengthwise, or 2 tsp. vanilla bean paste or vanilla extract
• 1¼ cups whole milk
• ½ cup heavy cream
• Kosher salt
• 1 day-old medium loaf brioche, sliced 1½"-thick
• 3 Tbsp. (or more) unsalted butter, divided
• Fleur de sel or flaky sea salt

Steps

1. Heat ¾ cup plus 1 Tbsp. heavy cream in a small saucepan over low heat until warm. Leave over low heat to keep warm until ready to use.
2. Meanwhile, heat 1 cup (200 g) granulated sugar in a large skillet over medium heat, swirling pan if needed, until melted, 5–7 minutes. Continue to cook caramel, swirling pan occasionally, until deep mahogany and wisps of smoke rise from the surface (the bubbling will lessen slightly too), 8–12 minutes more. (Caramel will go from perfectly caramelized to burnt very quickly so watch carefully. It is better to skew toward over caramelized than under here.)
3. Whisking constantly, carefully pour warm cream into caramel; remove pan from heat and stir in 6 Tbsp. unsalted butter, cut into small pieces. Let cool slightly, then season with fleur de sel or kosher salt. Set salted caramel sauce aside. Do Ahead: Sauce can be made 1 week ahead. Transfer to an airtight container; cover and chill. Reheat over low before using.
4. Vigorously whisk together 1¼ cups chilled heavy cream, ¼ cup mascarpone, and ¼ cup (28 g) powdered sugar in a medium bowl until soft peaks form. Scrape in seeds from ½ vanilla bean, split lengthwise; discard pod or reserve for another use. If using 2 tsp. vanilla bean paste or vanilla extract instead, add and then taste and add more as desired if needed. Set whipped mascarpone cream aside. Do Ahead: Whipped mascarpone cream can be made 1 day ahead. Cover and chill.
5. Whisk 4 large eggs and ⅓ cup (67 g) granulated sugar in a large bowl until frothy. Scrape in seeds from ½ vanilla bean, split lengthwise; discard pod or reserve for another use. Or add 2 tsp. vanilla bean paste or vanilla extract. Whisk until smooth, then add 1¼ cups whole milk, ½ cup heavy cream, and a pinch of kosher salt and whisk custard until no streaks of unincorporated egg remain. Working with 1 slice at a time, submerge 1 day-old medium loaf brioche, sliced 1½"-thick, in custard and let soak long enough to saturate but not so long that they fall apart. Transfer to a rimmed baking sheet.
6. Melt 2 Tbsp. unsalted butter in a skillet over medium heat. Working with 2 or 3 slices, cook bread until golden brown underneath, 2–5 minutes. Turn, reduce heat to medium-low, add 1 Tbsp. unsalted butter, and cook until browned on other side, 2–5 minutes. Transfer to plates. Repeat with remaining bread over medium-low heat, working in batches of 2 or 3 slices and adding more butter to pan as needed.
7. Top pain perdu with a dollop of whipped mascarpone cream, then spoon salted caramel sauce over and sprinkle with fleur de sel or flaky sea salt.