1.Prepare crust.Preheat oven to 425 degrees.roll pie crust into a circle on a 13 inch circle on a lightly floured surface.Fit into a 9 inch pie plate,fold edges under and crimp.Prick bottom and sides with a fork.Line piecrust with parchment paper;fill with pie weights or dried beans.Bake 9 minutes.Remove weights and parchment paper.
Whisk together egg yoke,and cream,brush bottom and sides of crust with yoke mixture.bake 6-8 more minutes or until crust is golden.Transfer to wire rack,ans cool.Reduce oven temperature to 350 degrees.
Prepare filling;Stir together melted butter,1 cup sugar,and next2 ingredients in a large bowl until mixture is well blended.Add sweet potatoes and next 4 ingredients;stir until mixture is well blended.Pour sweet potato mixture into prepared piecrust.( pie will very full)
Bake at 350 degrees for 50-55 minutes or until a knife inserted in the center comes out clean,shielding with aluminum foil to prevent excessive browning.Transfer pie to wire rack.and cool completely(about 1 hour)
Prepare meringue:Beat egg whites and next two ingredients at high speed with heavy duty electric stand mixer until foamy.Gradually add sugar,one tablespoon at a time,beating until stiff peaks form.
Beat one-forth of marshmallow creme into egg whites mixture;repeat 3 times with remaining marshmallow creme,beating until smooth(about 1 minute)Spread over pie.
Bake at 400 degrees for 6-7 minutes or until meringue is lightly browned. Note:Pie can be made up to a day ahead.Prepare recipe as directed through step 4: cover and chill up to 24 hours.Proceed as directed in steps 5 through 7.