To prepare crust: Preheat oven to 325 degrees F.

Coarsely chop walnuts in a food processor. Add graham cracker crumbs and process until the mixture looks like fine crumbs.

Whisk egg white in a medium bowl until frothy. Add the crumb mixture, butter, oil and salt; toss to combine. Press the mixture into the bottom and 1/2 inch up the sides of a 9-inch removable-bottom tart pan. Set the pan on a baking sheet. Bake until dry and slightly darker around the edges, about 8 minutes. Cool on a wire rack.

To prepare filling: Beat cream cheese, sour cream and 1/4 cup maple syrup in a medium bowl with an electric mixer on low speed until smooth. When the crust is cool, spread the filling evenly into it, being careful not to break up the delicate crust. Arrange blueberries on the filling, pressing lightly so they set in. Drizzle the remaining 2 tablespoons maple syrup over the berries. Chill for at least 1 hour to firm up.

Tip: To toast walnuts, spread on a baking sheet and bake at 350 degrees F, stirring once, until fragrant, 7 to 9 minutes.

Note: To avoid trans fats, look for graham crackers without partially hydrogenated vegetable oil. To make crumbs, pulse graham crackers in a food processor or place in a large sealable plastic bag and crush with a rolling pin. (You'll need about 14 whole-wheat graham cracker squares to make 1 cup of crumbs.)

MAKE AHEAD TIP: Refrigerate for up to 1 day. | Equipment: 9-inch removable-bottom tart pan