Preheat oven to 375°F.
Cream the softened butter and maple sugar together until smooth.
Mix in dry ingredients (except for oats) until well combined.
Mix in the wet ingredients (except for the egg) until well combined.
Gently mix in egg and once well incorporated, mix in the oats until a cohesive dough is formed.
Using a large scoop, scoop individual cookies onto a lined cookie tray with a generous amount of space between them. Scooping 6 large cookies per tray or 8 slightly smaller cookies are great options to choose from depending on desired sizing for the cookies.
Bake cookies for 10 minutes (until edges are golden brown)
Allow cookies a few minutes to cool, as they will be soft and can easily break.
Once cooled a bit, move them to a cookie rack to finish setting.
Mix together the cream filling by combining all ingredients.
Pipe the icing onto one cookie and sandwich it together using a second cookie. Repeat until all cookies are filled & enjoy!