Mix the milk and vinegar. In a large mixing bowl, combine warm milk and vinegar. Let it sit for about 5 minutes until it slightly curdles. This will create a quick buttermilk substitute that helps the cake stay soft and fluffy.
Add wet ingredients. Whisk in the sugar and vanilla extract until the sugar completely dissolves.
Add dry ingredients. Sift in the flour, baking powder, ground cinnamon, and salt. Gently fold or whisk until you get a smooth, lump-free batter.
Pour in the melted butter or oil and mix until everything is well combined. The batter should be smooth and slightly thick.
Carefully pour the cinnamon batter over the cooled caramel pecan layer in your prepared cake pan. Spread it out evenly with a spatula.
Optional crunch topping. Sprinkle about 1 tablespoon of cane sugar, caster sugar, or cinnamon sugar on top of the batter for an extra sweet, crunchy layer after baking.
Place the cake pan on a baking tray (to catch any caramel overflow) as shown in recipe photos and bake in a preheated oven at 180°C (350°F) for 40–42 minutes, or until the cake is golden and firm to the touch.
Let the cake cool in the pan for no longer than 10 minutes. Cooling it longer may cause the pecans to stick to the bottom.
Gently loosen the edges with a spatula, then flip the cake onto a serving plate or cake stand. Gently tap the pan’s bottom to help release it.
Finishing touches. If any pecans stick to the pan, simply lift them off with a spatula and place them back on top of the cake.
Allow the cake to cool completely before slicing and serving. Serve at room temperature or warm with a scoop of icecream.