Prepare your oven and equipment. Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. This prevents sticking and ensures even baking.
Cream the butter and sugars together in a large bowl using an electric mixer on medium speed for about 3 minutes, until light and fluffy. This incorporates air for a better texture.
Add the molasses, eggs, and vanilla to the butter mixture, beating until well combined. Scrape down the sides of the bowl to ensure everything is evenly incorporated.
Combine all dry ingredients (flour, baking soda, salt, ginger, cinnamon, nutmeg, and cloves) in a separate bowl and whisk together to evenly distribute the spices.
Gradually add the dry ingredients to the wet ingredients on low speed, mixing just until combined. Overmixing will develop too much gluten, making tough cookies.
Fold in the oats by hand using a rubber spatula until evenly distributed throughout the dough. The dough will be thick but still slightly tacky.
Scoop rounded tablespoons of dough (about 1.5 tablespoons per cookie) onto the prepared baking sheets, spacing them 2 inches apart. These will spread while baking.
Bake for 10-12 minutes until the edges are just set but the centers still look slightly underdone. The cookies will continue cooking on the hot baking sheet.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. This prevents breaking while they’re still soft.
Make the cream filling by beating the softened butter until creamy, then gradually adding the powdered sugar, vanilla, salt, and heavy cream. Beat for 3-4 minutes until light and fluffy.
Assemble the sandwich cookies by spreading or piping about 1-2 tablespoons of filling onto the flat side of one cookie, then pressing another cookie on top. Apply gentle, even pressure to spread the filling to the edges.
Let cookies set for about 30 minutes before serving to allow the filling to firm up slightly. This creates the perfect texture contrast between cookie and filling.