How to Make It
Preheat oven to 350°F. Beat butter and sugars with a heavy-duty stand mixer on medium speed until creamy, about 2 minutes; add eggs and vanilla, and beat until just combined. Whisk together flour, baking soda, salt, and cinnamon in a small bowl; gradually add to butter mixture, beating on low speed just until combined, about 10 seconds. Stir in oats and pecans.
Using a 1 1/2-inch cookie scoop, drop spoonfuls of dough 3 inches apart on parchment paper-lined baking sheets. (Or use your hands to shape dough into 2-inch balls.) Bake in preheated oven until golden but still soft in center, 9 to 10 minutes. Cool 1 minute on baking sheets; remove cookies to wire racks, and cool completely, about 20 minutes.
Pipe or spread about 1 1/2 tablespoons Salted Caramel Buttercream on 1 flat side of half of cooled cookies; top with remaining cookies, flat side down, pressing gently.