In the bowl of stand mixer fitted with paddle attachment (or using an electric hand mixer), cream together butter and sugar. Add egg and vanilla and mix until smooth. Scrape down bowl as needed.
In another bowl whisk together salt, baking powder, and flour. Add dry mixture to mixing bowl in two additions, alternating with coconut milk. Mix until just combined, and there are no longer any dry streaks of flour. Batter will be thick.
Spoon batter into jackfruit lined cake pan. Use the back of spoon or a mini offset spatula to spread batter into an even layer.
Bake for 35-40 minutes until toothpick inserted in center of cake comes out clean. Remove cake from oven and allow it sit for 5 minutes. Run a mini offset spatula or knife along the perimeter of cake to loosen from pan. Place serving plate over cake tin. Invert to release cake. Allow cake to cool for 15 minutes before slicing
Serve cake warm or at room temperature. Store any leftover cake in an airtight container in the fridge for up to 4 days.