Preheat oven to 350˚F. Process pretzels in a food processor until they form fine crumbs.
Add brown sugar, pulse until blended. With processor running, pour butter through chute until just blended.
Press crumb mixture into a lightly greased 9 inch spring form fluted pie plate.
Bake 12-15 minutes or until lightly browned.
Remove from rack and let cool for at least 30 minutes.
Stir together sugar, lemon zest and cornstarch in a small saucepan. Gradually add 1 cup water, whisking until smooth. Bring to a boil, whisking constantly. Boil, whisking constantly, 1 minute or until thickened. Remove from heat and add gelatin, whisking until gelatin dissolves. Cool 15 minutes.
Toss blueberries and gelatin mixture in a large bowl. Spoon into prepared crust. Cover loosely, chill 3 hours or until set.
In a large bowl, add heavy cream, vanilla and confectioners' sugar. With a hand mixer whip until thick and creamy.
Dollop cream in center of chilled pie, leaving some of the blueberries exposed.