Preheat the oven to 175 degrees Celsius. Line or grease a 16 or 18 cm spring form.
Making the lingonberry sauce by placing all ingredients in a small pot and bring to a boil. Lower the heat and let it simmer until it has thickened and the lingonberries are soft.
Meanwhile combine oat flour, rice flour, sugar, cardamom, baking soda, baking powder and salt in a bowl.
Add apple sauce and coconut oil and mix until crumbly. Reserve about 1 dl of the crumble for the topping.
Combine filmjölk, egg, vanilla extract and mashed banana until smooth.
Fold in the dry ingredients to the wet. Mix until you have a smooth mixture.
In a separate bowl add the ingredients for the sour cream topping and whisk until smooth.
Pour the batter into the prepared pan.
Dollop lingonberry jam and sour cream batter over the cake and make big swirls using a knife. Sprinkle with the offset crumble evenly over the cake.
Bake in the middle of the oven for 38-45 minutes.
Remove from the oven and let it cool completely before slicing it.