Heat oven to 350 degrees F. In large bowl, stir cookie mix, softened butter, water, vanilla and egg with wooden spoon until soft dough forms. Press dough evenly into bottom and sides of ungreased 9- or 10-inch tart pan with removable bottom. Prick dough all over with fork.

Bake 15 to 20 minutes until edges are light golden brown (dough will puff up during baking). Transfer to cooling rack. Using bottom of shot glass or drinking glass, press cookie crust down to within 1/2 inch of edges. Cool completely in pan, about 1 hour.

In small saucepan, sprinkle gelatin evenly over lemon juice. Let stand 1 minute, then stir gently over low heat 1 to 2 minutes until gelatin is dissolved. Whisk in buttermilk and honey. Set aside to cool slightly.

In medium bowl, beat heavy cream with electric mixer on high speed 1 to 2 minutes until stiff peaks form. Fold cooled buttermilk mixture into whipped cream until just combined. Pour and spread mixture evenly into cooled cookie crust. Cover and refrigerate 2 hours or until filling is set. Carefully remove tart from side of pan before serving.