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Place chopped macadamias on a parchment-lined baking tray. Heat sugar and water in a small pan over low heat until the sugar dissolves. Increase heat to medium and simmer until caramel turns amber, about 4–5 minutes. Pour caramel over macadamias. Let cool, then break into shards.
Grease a 22–23cm fluted tart pan and line the bottom with parchment paper. Blitz cookies to fine crumbs and mix with cinnamon and sea salt. Stir in melted butter until mixture resembles wet sand. Press evenly into the prepared pan. Chill to set.
Soften ice cream in the fridge for 15 minutes. Scoop into the tart shell, pressing to fill. Freeze until firm.
Combine egg whites, sugar, and salt in a metal bowl. Place over a simmering pot of water, whisking until sugar dissolves and the mixture reaches 71°C (160°F). Whisk in a stand mixer on high speed until glossy, stiff peaks form, about 7–8 minutes. Add vanilla and whisk briefly.
Remove pie from tart pan and place on a cake stand. Spoon meringue onto the pie, creating peaks. Toast with a kitchen blowtorch. Decorate with macadamia praline shards. Serve immediately.