Preheat oven to 325 degrees. Lightly butter two 10.5 x 15.5 inch jelly roll pans and line the bottoms with parchment paper. Butter the paper. Dust the pans with matza cake meal, tapping out any excess.
In a large bowl, using an electric mixer, beat the egg whites with 1/2 tsp. of the cream of tartar at high speed until peaks form. Add 1/2 cup of the confectioners sugar and beat at high speed until stiff and glossy.
In another large bowl, beat the egg yolks until pale, about 2 minutes. Add the cake meal, 3 tbsp. cocoa, 1/2 c. of the confectioners sugar and 1 tsp. vanilla and beat at low speed until combined. Beat in a fourth of the egg whites, then fold in the remaining whites until no streaks remain.
Pour the batter into the prepared pans and spread in a thin, even layer. Bake the cakes for 6 minutes, until firm and slightly puffed. Transfer the pans to a rack and let cool for 5 minutes.
Run the tip of a knife around the edge of the cakes. Dust the cakes with cocoa and cover each one with a sheet of wax paper slightly larger than the pan. Invert cakes onto the wax paper and remove pans. Cover cakes with plastic wrap to keep moist.
In a small bowl, combine 2 tbsp. of very hot water with 2 tbsp. of the granulated sugar and stir until the sugar is dissolved. Let the sugar syrup cool to room temperature.
In a small sauce pan, combine the remaning 1/2 c. of granulated sugar and 1/4 tsp. of cream of tartar with 3 tbsp. water and cook over med-high heat, washing down the sides od the pan with a wet pastry brush and gently swirling the pan, until a deep amber caramel forms, about 6 minutes, Remove from heat.
Add 1/4 c. plus 2 tbsp of the heavy cream and the butterand tir until just combined, Cook over high heat for 1 minutes. Transfer the caramel sauceto a heatproof bowl and let cool completely.
In a large bowl, using an electric mixer, combine the remaining 1 c. heavy cream with 1/4c. of confectioners sugar and 1/2 tsp. vanilla. Beat in the sour cream and salt, then beat until firm peaks form. Fold in the cooled caramel sauce and refrigerate.
Peel the parchment paper off both cakes and brush the surfaces with the sugar syrup. Spread the caramel cream over each cake in a thin, even layer. Keep the long side nearest you, and roll up each cake, using the wax paper to help you form a tight roll. Wrap the rolls in the wax paper, transfer to a baking sheet and freeze until very firm, about 2 hours.
Melt the chopped chocolate in a medium-size microwave safe bowl. Whisk in the oil. Let the glaze cool slightly. Line a baking sheet with wax paper. Unwrap the rolls and cut each one into 5 pieces. Working quickly, dip both ends of each roll into the chocolate glaze, then dip the tops and bottoms, letting any excess glaze drip back into the bowl. Place the rolls on the prepared baking sheet and refrigerate just until the glaze sets completely. Serve the yodels cold or at room temperature.
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