How to Make It
Preheat the oven to 350°. Butter a 10-by-15-inch jelly roll pan and line it with parchment paper, then butter the paper. In a medium bowl, beat the egg yolks with 1/4 cup of the granulated sugar and the vanilla until fluffy, about 3 minutes. Using a rubber spatula, gently fold in the flour.
In a clean bowl using a clean whisk, beat the egg whites with the salt at medium speed until soft peaks form. Gradually add the remaining 1/4 cup of granulated sugar and beat until the whites are glossy. Using a rubber spatula, fold the whites into the yolk mixture until no streaks remain. Quickly fold in the melted butter. Spread the batter in the pan. Bake in the lower third of the oven for 20 minutes, or until golden and puffy. Let cool in the pan on a rack.
Run the blade of a knife around the edge of the cake pan. Dust the cake with the confectioners' sugar and cover with a sheet of plastic wrap and a clean kitchen towel. Top with a cutting board and, holding both the board and pan, invert the cake. Rap the board against the table, then remove the pan and carefully peel off the paper.
In a large bowl, whip the cream with the granulated sugar, vanilla and salt to stiff peaks. Using an offset metal spatula, spread the raspberry jam on the cake. Spread the whipped cream evenly over the jam. Begin rolling up the cake from the long side, as tightly as possible, using the kitchen towel and plastic wrap to help shape the roll. Wrap the roll tightly in the plastic and transfer to a baking sheet. Refrigerate for at least 6 hours or, preferably, overnight.
Put the chocolate in a bowl. In a saucepan, stir the cream, milk and sugar over moderate heat just until the sugar is dissolved. Pour the hot cream over the chocolate; let stand until the chocolate is melted, 3 minutes. Whisk until smooth, then whisk in the butter and let cool slightly.
Discard the plastic wrap and transfer the cake to a rack. Pour half of the chocolate glaze all over the top and sides and spread it evenly with an offset spatula. Spread the remaining glaze all over the cake and refrigerate until set, at least 2 hours. Garnish the top with raspberries. Transfer the cake to a platter, cut into slices and serve.