Preheat the oven to 180°C (350°F) and line two cupcake trays with cupcake papers.
Add the oil, eggs, and sugar to a bowl of a stand mixer fitted with a whisk attachment. Beat on medium-high speed until combined, about 2 minutes.
Sift together the salt, cinnamon, and flour then add the flour mixture to the egg and sugar mixture. Beat at low speed until just combined.
In a jug combine the milk and vanilla, and slowly pour this into the cupcake batter with the mixer's motor running at low speed. Scrape down the sides of the bowl and mix again, making sure it is lump-free.
Combine the extra sugar and ground cinnamon in a small bowl, and ensure it is well-mixed.
Fill each cupcake liner a third of the way up with the cupcake batter. Sprinkle a tablespoon of the cinnamon sugar mixture over the batter, and pour more cupcake batter over this to fill them ⅔ of the way up the liner. Use a skewer to swirl through the cinnamon sugar.
Bake in a preheated oven for 12 – 15 minutes or until a toothpick inserted into the center comes out clean. Cool completely on a wire rack.
Cinnamon Buttercream
In a bowl of an electric mixer fitted with a paddle attachment, add the butter and icing sugar. Beat at medium speed until the mixture looks like fine breadcrumbs.
In a jug combine the milk and vanilla, with the mixer's motor running at low speed slowly add the milk mixture. Continue until it has all been added. Then increase the speed of the mixer to medium-high. Beat until light and fluffy, scraping down the sides of the bowl often.
With the mixer's motor running at medium-low speed, add the dulce de leche to the frosting and beat to combine. Scrape down the bowl and beat again at medium-high speed.
Fill a prepared piping bag with the caramel and cinnamon frosting and pipe a swirl onto each cupcake. Decorate the top of each cupcake with a mini gingerbread cookie. Enjoy!