In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugar at medium speed until fluffy, 3 to 4 minutes, stopping to scrape down sides of bowl. Add egg yolk, beating well after each addition. Add condensed milk and vanilla extract, beating just until combined.
In a medium bowl, whisk together flour, ground raspberries, rice flour, salt, baking powder, and baking soda.
With mixer at low speed, gradually add flour mixture to butter mixture, beating just until combined. Add in food coloring and beat until just combined. Cover tightly with plastic wrap; refrigerate for 1 hour.
Preheat oven to 300°. Place oven rack in lower third of oven. Line 2 large rimmed baking sheets with parchment paper.
On a lightly floured surface, roll disk to ¼-inch thickness. Using a 2½-inch fluted round cutter, cut dough. Place 2 inches apart on prepared pans.
Bake until top is dry, 15 to 20 minutes. Let cool on pans for 5 minutes. Remove from pans and let cool completely on wire racks.
Spoon Vanilla Buttercream into a piping bag fitted with a ¼-inch French-star piping tip*. Pipe a border of buttercream onto flat side of half of cookies. Spoon raspberry jam into a piping bag; cut a ¼-inch tip on the end. Fill center of buttercream border with raspberry jam. Gently place remaining cookies, flat side down, on top of filling. Carefully press sandwich cookies together (use light pressure to prevent cracking). Cookies are best served the same day. Store in an airtight container at room temperature for up to 3 days.
Recipe by Victoria at https://victoriamag.com/raspberry-shortbread-creams/