Place the kataifi on a clean, dry cutting board. Using a sharp knife, chop it into short, fine strands, about 1 inch/2.5 cm long. In a wide nonstick skillet over low heat, melt the butter completely. Add the kataifi and stir continuously with a wooden spoon or silicone spatula, ensuring every strand is evenly coated in butter. Continue stirring over low heat until lightly golden, about 10 to 12 minutes. Add the powdered sugar and continue to stir for another 5 to 7 minutes, until the mixture is deeply golden and caramelized. The texture should be crisp, not soggy. Set aside to cool completely.

For the pistachio layer, whip the cream in a stand mixer fitted with the whisk attachment until soft peaks form, about 2 to 3 minutes. Add the condensed milk and pistachio paste and beat until the mixture is thick and fully combined, about 30 seconds more. Do not overwhip.

Line two standard loaf pans (8½ x 4½ inches/21 x 11 cm) or one 8-inch/20 cm springform pan with parchment paper, leaving a generous overhang for easy removal. Press one-third of the cooled kataifi mixture into the bottom, smoothing and compacting it with the back of a spoon or an offset spatula. Freeze for 10 minutes.

Gently pour the pistachio ice cream mixture over the kataifi base, smoothing the top with a clean spatula. Freeze for 1 hour, uncovered, until firm.

While the pistachio layer chills, make the ricotta layer. Clean the mixer bowl and whisk attachment, then whip the cream to soft peaks. Add the sweetened condensed milk and ricotta, and whip until the mixture is smooth and light, about 30 seconds. Scrape the sides and bottom of the bowl to ensure everything is evenly incorporated.

Once the pistachio layer is set, sprinkle another third of the kataifi over the surface and gently press to level it without disturbing the frozen layer underneath. Pour the ricotta mixture on top, smoothing it out evenly. Finish with the remaining kataifi, pressing down gently to secure it into the surface.

Freeze the assembled cake overnight, uncovered if possible, or cover once solid. The longer it freezes, the cleaner the slices.

When ready to glaze, combine the white chocolate and canola oil in a microwave-safe bowl. Microwave in 30-second bursts, stirring between each, until fully melted and smooth. Stir in the pistachio paste until fully incorporated.

Remove the cake from the pan using the parchment overhang and transfer it to a serving plate. Pour the pistachio glaze evenly over the surface and sides, allowing it to drip naturally. Freeze for another hour until the glaze is set.

Before serving, garnish with additional kataifi, chopped pistachios, or edible rose petals, if desired. Slice with a warm knife and serve frozen.

The cake can be stored in the freezer for up to 1 week, well wrapped.