Preheat the oven to 350°F (175°C). Line two large baking sheets with parchment paper or spray them lightly with nonstick cooking spray.

In a medium-sized bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, beat the softened butter and 1½ cups sugar on medium-high speed until pale and fluffy, approximately 2 to 3 minutes.

Reduce the mixer speed to medium and incorporate the egg, vanilla extract, and reserved vanilla bean seeds. Mix until well combined, about 30 seconds.

Lower the mixer speed to low and gradually add the dry flour mixture. Beat just until the dough is fully combined, scraping down the bowl as needed.

Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them approximately 2 inches apart. Bake for 7 to 8 minutes, rotating the sheets halfway through. Allow the cookies to cool completely on the parchment placed over wire racks.

In the bowl of a food processor fitted with the metal blade, purée the raspberries and remaining 2 teaspoons sugar. Strain the mixture through a fine sieve set over a small bowl, pressing to extract the juice. Discard the seeds and set the strained juice aside.

Place the chopped white chocolate in a heatproof bowl set over a pan of simmering water (double boiler method) and stir until melted. Remove from heat and gradually whisk in the heavy cream in a slow stream, followed by the reserved raspberry juice. Chill the filling in the refrigerator for approximately 30 minutes, or until it has thickened to a spreadable consistency.

Spread approximately 1 rounded teaspoon of the raspberry cream filling on the flat side of one cooled cookie. Top with a second cookie to form a sandwich. Repeat with the remaining cookies and filling.

Store the completed sandwich cookies in an airtight container at room temperature for up to 3 days or refrigerated for up to 5 days.