Preheat the oven to 180°C (350°F). Grease the cake pan with butter or line with parchment paper.
Prepare the caramel layer: Melt butter and mix with brown sugar. Pour into the bottom of the cake pan, then arrange pineapple rings and place a cherry in the center of each.
Combine dry ingredients: In a bowl, mix spelt flour, desiccated coconut, baking powder, and salt.
Cream butter and erythritol until light and fluffy. Add eggs one at a time, then mix in yogurt and vanilla extract.
Add dry ingredients to wet mixture and gently fold until just combined.
Pour batter over the pineapple layer and spread evenly.
Bake for 35–40 minutes or until a toothpick comes out clean.
Cool for 10 minutes, then flip onto a plate and let it cool completely before serving.