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Step 1
Prep oven and pan
Preheat to 350°F / 175°C. Grease a 9-inch round cake pan and line the bottom with parchment.
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Step 2
Prepare apples
Core and cube the apples, then toss them with apple cider vinegar.
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Step 3
Mix dry ingredients
Mix flour, baking powder and salt in a small bowl.
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Step 4
Beat butter, sugars and eggs
Beat butter with the white and brown sugar until light; beat in the eggs one at a time until smooth.
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Step 5
Finish batter
Mix in rum, vanilla and the flour mixture in two additions, then fold in the apples.
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Step 6
Bake
Transfer batter to the prepared pan, smooth the top, sprinkle with sugar and bake until a skewer comes out clean.
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Step 7
Cool and serve
Cool in the pan, turn out carefully, then dust with powdered sugar if desired.