The most extraordinary Oatmeal Sandwich Cookies made by preheating oven to 350°F lining baking sheets combining 2 cups old-fashioned rolled oats 1 cup flour 1 tsp cinnamon 1/2 tsp baking soda and 1/2 tsp salt beating 3/4 cup softened butter 3/4 cup packed brown sugar and 1/4 cup granulated sugar medium-high 2 minutes adding 1 room temperature egg and 2 tsp vanilla mixing combined adding oat flour mixture on low just combined scooping precisely uniform 1 1/2 tbsp portions 2 inches apart baking 350°F 10 to 12 minutes until edges set and lightly golden and centers still slightly soft cooling completely on sheet then beating 8 oz room temperature cream cheese until silky adding 2 cups sifted powdered sugar 1 tsp cinnamon 1 tsp vanilla and pinch salt beating incredibly fluffy adding cream one tbsp at a time for proper piping consistency matching cookies in uniform pairs piping generous filling over flat bottom of one pressing matching cookie over gently. A completely perfect chewy rolled oat butter brown sugar egg vanilla cream cheese cinnamon filling sandwich cookie recipe.