Preheat the oven to 350°F (180°C).
In a bowl, cream together the butter and sugar for 1 minute and then add in the eggs, vanilla extract and canola oil. Mix until well combined.
3/4 cup salted butter, softened, 3/4 cup granulated sugar, 1 egg + egg yolk, 1 1/2 tsp vanilla extract, 2 Tbsp canola oil
Add in the flour, baking powder and cinnamon, mixing until a soft dough forms.
2 1/4 cups all-purpose flour, 1 1/2 tsp baking powder, 1/2 tsp ground cinnamon
Scoop the cookie dough out using a #40 scoop (1 1/2 Tbsp of dough). Roll into a ball and flatten just slightly before rolling and coating the cookie dough in the cinnamon sugar mixture. Arrange on a parchment or silicone lined cookie sheet.
Cinnamon Sugar Mixture: 1/4 cup granulated sugar + 1/2 tsp ground cinnamon
Bake for 9-11 minutes. The cookies will spread and the center of the cookie should look puffed up and no longer wet before taking them out of the oven.
While the cookies are cooling, make the base buttercream frosting by whipping the butter until smooth.
1/2 cup salted butter, room temperature
Add the powdered sugar, one cup at a time, adding a little bit of milk after each cup of powdered sugar to keep the consistency like a thick frosting.
3 cups powdered sugar, milk, to thin
Once you have added all of the powdered sugar, mix in the cinnamon thoroughly.
1/2 Tbsp ground cinnamon
Add the frosting to a piping bag fit with a small round piping tip. Pipe the frosting onto the warm cookies in a spiral. Start in the center of the cookie and work your way out.
Sprinkle some extra cinnamon and sugar on top- serve warm!