Preheat the oven to 340°F.
In a saucepan, melt the butter, sugar, and syrup together until it starts to foam. Reduce the heat and let it thicken. Remove from heat and add the cinnamon and salt. Fold in the chopped pecans.
Mix the milk and vinegar together and set aside for 10 minutes.
Add the remaining wet ingredients to the milk mixture.
Sift in the dry ingredients and gently mix until just combined.
Pour the caramel pecan topping into a lined springform pan and spread it evenly. Pour the cake batter on top of the pecans and bake for 40-50 minutes, or until well-risen and cooked through.
Flip the pan onto a serving plate and let the cake cool before slicing.