Preheat oven to 350°F. Line two baking sheets with parchment.
Beat 1 cup butter with 1/2 cup powdered sugar until light and creamy, about 2 minutes.
Mix in 2 tsp vanilla and 1/2 tsp salt until smooth.
Add flour and cornstarch. Blend on low just until a soft dough forms and clumps together.
Scoop 1-tbsp portions, roll into balls, and set 2 inches apart. Gently flatten to about 1/4 inch thick.
Bake 12–14 minutes, until edges are set and just turning pale gold. Cool 5 minutes, then move to a rack.
Cream 1/2 cup butter until smooth. Gradually beat in 1 3/4 cups powdered sugar.
Blend in raspberry jam, lemon juice, 1/2 tsp vanilla, and a pinch of salt. Add cream as needed for a spreadable frosting.
Pair cookies by size. Pipe or spread about 1 tbsp filling on one cookie and cap with its partner.
Chill sandwiches 10 minutes to set. Serve or store airtight.
Notes
Variation: Add 2 tbsp finely crushed freeze-dried raspberries to the filling for extra berry punch. Storage: Keep cookies airtight at cool room temperature for 2 days, or refrigerate up to 5 days. For crisp edges, assemble the day you serve.This recipe is an original creation inspired by classic Raspberry Cream Sandwich Cookies flavors. All ingredient ratios and instructions are independently developed.