Preheat the oven to 350°F (180°C). Lightly grease 2 (6-inch) round cake pans, and line the bottoms with parchment paper.

For the cake layers: Add the flour, brown sugar, baking powder, baking soda, and salt to the bowl of a stand mixer and mix to combine. Add the butter, and with the flat beater attached, mix on medium speed until the butter is mixed in and the mixture resembles fine bread crumbs.

With the mixer on medium speed, add the eggs, one at a time, followed by the buttermilk and the oil. Continue mixing until the batter is smooth. Divide between the two pans (about 1½ cups or 322 grams each) and spread evenly.

Bake until the cakes spring back to a light touch and they are starting to come away from the sides of the pans, about 25 minutes. Remove and set aside for 15 minutes before turning out onto a wire rack to cool completely.

For the frosting: Add the butter and cream cheese to the bowl of your stand mixer and, with the flat beater attached, beat on medium speed until smooth and creamy. Slowly add in the confectioners’ sugar on low speed. Once all has been combined, turn up the speed to medium, and beat until light and fluffy, about 2 minutes. Add the dulce de leche and salt, and beat just until combined.

To assemble the cake, pipe a ring of frosting around the edge of one of the cake layers to create a border. Spoon the dulce de leche into the centre, and spread into an even layer. Top the dulce de leche with a thin layer of frosting. Place the second cake layer on top and spread the remaining frosting over the top and sides of the cake. The cake will keep refrigerated for 3 to 4 days.