Preheat oven to 350°F. Grease an 8-inch springform pan and line bottom with parchment paper.
Pour prepared lava cake batter into pan. If a separate fudge-sauce packet is in box, squeeze sauce onto batter. Bake until just done, 25 to 30 minutes. Cool completely on a wire rack. Run a knife along inside of pan to loosen cake. Remove pan sides from cake and gently pull parchment to slide cake off pan bottom.
In a medium bowl, stir together mascarpone, coffee and sugar. Spread onto top of cake.
Hold white-chocolate bar directly over cake. Using a vegetable peeler, scrape shavings of white chocolate onto cake. Refrigerate cake until ready to serve. Garnish with whipped cream and raspberries, if desired.