German Chocolate Cake Roll

1. Position a rack in the center of the oven and preheat to 350ºF. Lightly grease a 13-by-18-inch jelly roll pan; line with parchment paper, letting it come up the short sides by about 2 inches. Brush the paper with oil or melted butter and lightly dust with flour.
2. Make the filling: Whisk the evaporated milk, 1 cup sugar, 3 egg yolks, and the cubed butter in a saucepan over medium heat. Cook, stirring constantly, until thick and creamy, about 10 minutes. Remove from heat; stir in 1 teaspoon vanilla, toasted coconut, and pecans. Set aside to cool completely, stirring occasionally.
3. Make the cake: Meanwhile, whisk the flour, baking soda, and salt in a medium bowl.
4. In another bowl, whisk the cocoa and chocolate. Add the hot coffee to the cocoa mixture, stirring until smooth; stir in the buttermilk and the remaining 2 teaspoons vanilla.
5. Using a mixer, beat the softened butter and remaining 1-1/4 cups sugar in a large bowl on high speed until fluffy, about 4 minutes. Reduce the speed to low; add the 3 whole eggs, 1 at a time, incorporating each one before adding the next. Add the flour mixture in 3 parts, alternating with the cocoa mixture in 2 parts, beginning and ending with the flour. Beat until just blended; if necessary, fold the batter together with a rubber spatula.
6. Spread the batter evenly in the prepared pan. Bake until cake springs back when pressed lightly, about 16 minutes. Cool slightly in the pan.
7. Run a knife around the edge and slide the cake with its paper onto a work surface. Spread the coconut filling evenly over the cake. Roll the cake from one of the short ends, pulling it away from the parchment into a tight cylinder; transfer to a platter. Cool completely and dust with the confectioners' sugar or cocoa.

Serves 8 to 12.