Mix flour, sugar, and salt together. Add egg yolks and cream; mix together. Put diced rhubarb into unbaked pie crust. Pour egg/flour/sugar mixture over rhubarb. Bake at 450 degrees for 15 minutes. Remove from oven and turn oven down to 350 degrees. For meringue, beat egg whites until stiff. Mix in sugar and lemon extract. Spoon over pie after removing from oven. Then bake at 350 degrees until golden brown.