Beat sugar and oil in a medium bowl until blended. Beat in egg, honey, and vanilla.
In a separate bowl, whisk together flour, baking powder, and salt. Gradually add flour mixture to sugar mixture and mix well. Cover and refrigerate dough for at least 2 hours.
Preheat oven to 350 degrees F. Grease a baking sheet or line with parchment paper.
Scoop out dough by tablespoonfuls, roll into balls, and place on prepared baking sheet. Using fingers, gently press down on each ball to flatten slightly. Bake for 8-10 minutes, or until bottoms are lightly browned. Cool for 1 minute before removing to a wire rack to cool completely.
Once the honey cakes have cooled completely, it’s time to make the filling. Place the butter in a bowl and beat with an electric mixer for 2-3 minutes until pale and creamy. Beat in the cream, then gradually add the sugar and the cinnamon. Continue beating for 2-3 minutes until the buttercream is light and fluffy.
To assemble, pipe or spread the buttercream on the flat side of half of the honey cakes. Top with the rest of the cakes. Allow to set before serving.