Preheat the oven to 350 degrees F (175 degrees C).
Combine 1 cup flour and sugar in a bowl. Cut in butter until mixture resembles coarse crumbs. Press crust into an ungreased 8-inch square baking pan.
Bake in the preheated oven until lightly browned, 15 to 20 minutes. Remove from oven, leaving heat on.
Combine sugar, 2 tablespoons flour, and salt in a bowl. Beat in egg yolks and heavy cream. Stir in rhubarb. Pour over the hot crust in the baking pan.
Return pan to the hot oven and bake 40 minutes.
Beat egg whites and vanilla extract together in a bowl at medium speed until soft peaks form. Gradually add sugar and beat meringue until stiff peaks form.
Remove pan from the oven, leaving heat on. Spread meringue over hot filling in the baking pan, spreading to seal edges. Sprinkle coconut on top.
Return pan to the hot oven and bake 15 minutes more.
