Preheat oven to 350°. In a large bowl with an electric mixer on medium speed, beat cake mix, flour, eggs and butter until well combined for 1.5 to 2 minutes. Fold in almonds. Divide the cake mixture in half. Shape each half into a 2-by-12-inch log on a large parchment-lined baking sheet.
Bake in preheated oven until golden brown and firm, about 25 minutes. Let logs cool on baking sheet for 15 minutes.
Transfer logs to a cutting board; cut each diagonally into 20 slices (½ inch thick), discarding end pieces. Place all 40 slices on parchment-lined baking sheets and bake until crisp, 8 to 10 minutes (turning over halfway through). Let biscotti cool on baking sheets for 5 minutes, then transfer to wire racks and let cool completely, about 20 minutes.
Dip biscotti halfway into melted white chocolate, placing on parchment-lined baking sheets; sprinkle with nonpareils. Let stand until chocolate is set, about 1 hour.