Make the sauce: Combine the raspberries, granulated sugar and lemon juice in a small saucepan and bring to a simmer over medium-high heat, mashing with a spoon. Press through a fine-mesh sieve into a bowl using the back of a spoon. Refrigerate until cold.
Make the mousse: Put the white chocolate and 1/4 cup heavy cream in a medium microwave-safe bowl. Microwave in 30-second intervals, stirring, until the chocolate is melted; whisk until smooth and creamy. Beat the remaining 1 3/4 cups heavy cream in a large bowl with a mixer on medium-high speed until foamy. Add the confectioners' sugar and vanilla; beat until soft peaks form, about 2 more minutes. Whisk about 1 cup of the whipped cream into the chocolate mixture, then fold in the rest until combined.
Divide half of the mousse among 6 small glasses; top each with about 1 tablespoon raspberry sauce and a few raspberries. Top with the remaining mousse, sauce and raspberries; sprinkle with shaved white chocolate. Refrigerate until cold, at least 30 minutes.