Cream unsalted butter with Truvia® Sweet Complete™ until smooth and fluffy, about 2–3 minutes. Mix in vanilla extract, kosher salt, and egg until combined. Gradually add sifted cocoa powder and all-purpose flour until a dough forms.

Shape dough into a disc, wrap in plastic wrap, and chill in refrigerator for 60 minutes. After chilling, roll out the dough to 1/4 inch thick and cut out circles. Chill cutouts again for 20 minutes.

Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper. Bake cooled cookie rounds for 9–10 minutes. Let cookies cool completely on a wire rack.

Simmer raspberries with Truvia and water in a saucepan over medium heat for 5–7 minutes. Strain mixture through a fine sieve. Beat softened butter with Truvia® Confectioner’s until creamy, then mix in the cooled raspberry juice and heavy cream until fluffy.

Pipe raspberry buttercream onto the center of one cookie and sandwich it with another cookie. Repeat until all cookies are filled.

Refrigerate assembled sandwiches for at least 30 minutes until buttercream is set. Store in an airtight container at room temperature or in the fridge for up to a week.