Pre-heat oven to 350 degrees and line two baking sheets with parchment paper.
In a medium bowl, whisk together flour, baking powder and salt.
In the bowl of an electric mixer or in a large bowl with a hand mixer, beat butter and 1 ½ cups sugar at medium-high speed until mixture is fluffy, roughly 2-3 minutes.
Add egg, vanilla extract, and vanilla bean seeds and mix until smooth. Reduce mixer speed to low and slowly mix in the flour mixture, taking care not to over-mix.
Scoop about 2 Tbsp of dough and form into a ball. Space 2 inches apart on prepared baking sheets. Bake for about 5 minutes. Remove baking sheets from over and gently tap on counter. Return to oven (try to put pans in different positions in oven when you return them). Bake for another 5-7 minutes.
Remove cookies from oven and let cool in pan for a couple minutes before moving to wire racks to cool completely.
While cookies are baking, puree raspberries and remaining tsp of sugar in a food processor. Push the puree through a sieve and into a small bowl allowing juices through. Set aside.
Place the white chocolate in a heatproof bowl placed tightly over a saucepan of simmering water (you can also use a double boiler). Stir chocolate until melted and remove from heat.
Slowly mix cream into the white chocolate. Whisk the raspberry puree in until fully combined. Place in the fridge for about 30 minutes.
Once chilled, spread raspberry filling on one side of a cooled cookie (face down) and sandwich with another cookie.
You can store cookies in an airtight container at room temperature for 2-3 days, however, I like to keep them in the fridge for maximum freshness.