Roast Pear and Blueberry Trifle with Custard

To prepare custard: Whisk eggs, 1/2 cup sugar, cornstarch, salt and 1/2 cup milk in a medium bowl until smooth. Heat the remaining 3 cups milk in a large heavy saucepan over medium heat until steaming. Gradually pour the hot milk into the egg mixture, whisking constantly. Return this mixture to the pan and cook over medium heat, whisking constantly, until the custard bubbles and thickens. (Use caution, as hot custard will sputter. ) Remove from the heat and stir in vanilla. Transfer the custard to a shallow glass dish. Press plastic wrap directly onto the surface and refrigerate until chilled, at least 1 hour or overnight.

To roast pears: Preheat oven to 400°F. Coat a rimmed baking sheet with cooking spray. Toss pears, 2 tablespoons sugar and lemon juice in a large bowl. Spread the pears on the prepared baking sheet. Roast the pears until tender and golden brown in spots, turning occasionally, 30 minutes.