For the crust, in a large bowl cream butter and sugar. Add egg yolks and sour cream, mix well. Combine flour and baking powder; gradually add to creamed mixture. Press into greased 13x9 baking pan; set aside.
For the filling, in a small saucepan, combine the flour, egg yolks and pineapple. Cook and stir over medium heat until mixture reaches 160 degrees and coats the back of a metal spoon. Remove from the heat and add the vanilla. Pour over the crust and bake in a 350 degree oven for 30 minutes.
For the topping, small mixing bowl, beat egg whites until soft peaks form. Gradually add powdered sugar and vanilla, beating until stiff peaks form. Spread over hot hot filling, sealing edges to the pan. Sprinkle with walnuts. Bake 15 minutes longer or until golden brown. Cool on wire rack for 1 hour and then refrigerate.