For the cake layers:
For The Cream:
1. Make the cream: in a small saucepan whisk eggs, sugar and cornstarch. Whisk until smooth. Add sour cream and whisk until combined and smooth.
2. Place the saucepan over medium-low heat and cook, stirring constantly for about 5-6 minutes, until thickens. Remove from heat, add butter and vanilla extract, stir until incorporated. let cool slightly and transfer to a piping bag.
3. Make cake crumb layers: in a large bowl mix flour, sugar and salt. Coat the butter with the flour mixture and grate to the bowl, then, crumble with your fingers until small crumbs are formed. Do it in two or three batches. Or you can do this in a food processor.
4. Transfer the crumbs to a large pan and cook over low heat, stirring frequently, until golden brown, about 15 Remove from heat.
5. Assemble: spread 1/4 of the crumbs in a 18cm (7-inch) cake ring/pan and lightly press to the bottom. Then gently pipe 1/4 of the cream to an even layer of, without destroying the crumb layer. Repeat this process for 3 more times.
6. Release from the ring. Spread a thin layer of cream on the sides of the cake. Sprinkle some white chocolate shaving on top.
7. Refrigerate for at least 2 hours before serving.