For Crust: MIX butter, brown sugar and vanilla thoroughly using an electric mixer. Gradually blend in flour and corn starch. Press into 9-inch ungreased springform pan.
BAKE in a preheated 350°F oven for 20 minutes or until lightly browned. Remove from oven. Increase oven temperature to 450°F.
For Filling: WHISK sugar, corn starch, lemon juice and eggs in a heavy sauce pan over medium heat.
COOK, stirring constantly for 8 to 10 minutes, or until thick. Stir in sour cream and butter. Immediately pour over hot crust.
For Meringue: BEAT egg whites and cream of tartar in large bowl with electric mixer until soft peaks form. Gradually beat in sugar until stiff peaks form.
MOUND the meringue evenly over the warm filling, spreading to edges of pan.
BAKE at 450°F for 5 to 6 minutes until lightly browned. Cool for at least 30 minutes before serving. Store leftovers in refrigerator.