In a medium bowl, whisk yolks and eggs together, and set aside.
In a large metal bowl or the top of a double boiler, combine lemon juice, butter, and sugar. Set the bowl over a saucepan of simmering water; whisk until butter melts and sugar dissolves.
Gradually whisk 1/3 of hot butter mixture into eggs, and whisk the egg mixture back into bowl with remaining butter mixture, and place this back over simmering water. Whisk constantly until custard thickens and thermometer inserted into mixture registers 180°F, about 5 minutes (do not boil). (If you don’t have a candy thermometer, wait until the mixture thickens and coats the back of a wooden spoon.)
Pour lemon curd through a strainer set over medium bowl. Place plastic wrap directly on surface of lemon curd; chill overnight. (Can be made up to 2 days ahead. Keep refrigerated.)
For Coconut Meringue Layer
Position rack in center of oven, and preheat oven to 325°F.
Line 17x11-inch rimmed baking sheet with parchment paper. Mix coconut, 1/3 cup sugar, flour, and salt in medium bowl. Using electric mixer, beat egg whites and cream of tartar in large bowl until soft peaks form. Gradually add remaining 1/3 cup sugar; beat until stiff but not dry. Fold coconut mixture into meringue just until incorporated. Spread meringue evenly over parchment on prepared sheet, covering completely. Bake until light golden and just springy to touch, about 20 minutes (meringue will be soft). Cool completely on baking sheet. (Can be made 1 day ahead. Cover tightly with foil; store at room temperature.)
Place sheet of waxed paper on work surface. Cut around edges of meringue to loosen. Invert meringue onto waxed paper. Peel off parchment. Cut meringue crosswise in half, then cut lengthwise in thirds, forming six 8 1/2x3 2/3-inch rectangles. Cut piece of cardboard into 8 1/2x3 2/3-inch rectangle; cover cardboard with foil. Place 1 meringue rectangle on cardboard.
Roughly divide lemon curd into sixths just by cutting into it with a knife. Spread 1/6 of lemon curd evenly over meringue piece. Top with second meringue rectangle; press to adhere. Spread 1/6 of lemon curd over. Repeat procedure with 3 more meringue rectangles and 1/6 of lemon curd each time. Top with remaining meringue rectangle. You will be left with 1/6 of the lemon curd (you get to snack on that!). Chill cake until firm, about 1 hour.
Garnish with fresh raspberries and a sprinkling of powdered sugar. Using serrated knife, cut cake crosswise into 12 slices. Transfer to plates.
Notes
*How to toast coconut: Preheat oven to 325° F. Spread coconut on a rimmed baking sheet in a thin layer and bake 5-10 minutes, stirring a couple of times, until the coconut is golden brown and fragrant.Make ahead: The lemon curd can be made 2 days in advance, and the meringue can be made 1 day in advance.