Step 1

Adjust oven racks to upper-middle and lower-middle positions and heat oven to 300 degrees. Line 2 baking sheets with parchment.

Step 2

Process Rice Krispies in blender until finely ground, about 30 seconds. Combine 4 tablespoons butter and cream in large bowl and microwave until butter is melted, about 30 seconds. Whisk in processed Rice Krispies and vanilla until combined. Let cool slightly, 5 to 7 minutes.

Step 3

Combine flour, cornstarch, and salt in medium bowl; reserve. Whisk sugar into cooled butter mixture until incorporated. Add remaining 12 tablespoons butter, whisking until smooth. Stir in flour mixture until combined.

Step 4

Transfer dough to pastry bag fitted with 1/2-inch star tip. Pipe 1-inch-wide and 1/2-inch-high dough rounds onto prepared baking sheets. Refrigerate dough until firm, about 30 minutes.

Step 5

Bake until set but not brown, 18 to 22 minutes, switching and rotating sheets halfway through baking. Let cool completely on sheets, about 15 minutes. Repeat with remaining dough. Serve. (Cookies can be stored at room temperature for up to 2 days.)