Rhubarb and Raspberry Crostata

INGREDIENTS

• 1 large egg, beaten
• Raw sugar
• Sweetened whipped cream or vanilla ice cream (for serving)
• 1 6 ounce container fresh raspberries
• 1/2 cup whole wheat flour
• 1/2 teaspoon kosher salt
• 1/3 cup sugar
• 1 1/2 tablespoons sugar
• 1/4 cup cornstarch
• 1 cup unbleached all-purpose flour
• 3/4 cup (1 1/2 sticks) chilled unsalted butter, cubed
• 1 tablespoon whole milk
• 1 large egg
• 4 cups 1/2"-thick slices rhubarb