Preheat your oven to 350°F (175°C).

Crush the pretzels finely using a food processor or smashing them in a sealed bag.

In a bowl, combine the crushed pretzels, 1/4 cup sugar, and melted butter. Mix until it looks like wet sand.

Press the mixture evenly into the bottom of a 9-inch springform pan. Bake for 8-10 minutes until slightly golden. Let it cool completely.

In a heavy-bottomed saucepan over medium heat, melt 1 cup sugar while stirring until it turns a deep amber color.

Once it reaches the desired color, remove it from the heat. Carefully stir in the cubed butter, then whisk in the warm cream until smooth. Add flaky sea salt and let it cool to room temperature.

Melt the dark, milk, and white chocolates in separate heatproof bowls over simmering water (double boiler). Stir until smooth and allow to cool slightly.

In a clean bowl, beat the egg whites until soft peaks form. Gradually add 1/4 cup sugar, beating until stiff peaks form. Set aside.

Divide the cold heavy cream into three bowls. Whip each bowl until soft peaks form.

Fold the melted dark chocolate into the first bowl of whipped cream, then fold in one-third of the beaten egg whites. Spread half of this mixture over the cooled pretzel crust.

Drizzle half of the salted caramel over the dark chocolate layer, swirling it lightly.

Fold the melted milk chocolate into the second bowl of whipped cream and then fold in the next third of egg whites. Spread this mixture over the salted caramel.

Add the remaining salted caramel as a thin swirl on the milk chocolate layer.

Fold the melted white chocolate into the last bowl of whipped cream and add in the remaining egg whites. Spread this mixture on top of the cake.

Cover the cake loosely with plastic wrap and refrigerate for at least 6 hours or overnight.

Carefully remove the cake from the springform pan. Garnish with extra pretzel pieces, chocolate shavings, and a sprinkle of flaky sea salt if desired.