For lemon-paprika mayonnaise, process yolks, lemon rind and garlic in a food processor to combine, then, with motor running, add combined oils in a thin steady stream, processing until thick and combined. Add lemon juice and paprika, season to taste and refrigerate. Makes about 250ml.
Heat butter in a saucepan over medium heat, add corn, onion, chilli and garlic and sauté until tender (4-5 minutes), season to taste, transfer to a large bowl and cool to room temperature. Add crab, mint, flour, polenta, baking powder and rinds, season generously to taste and stir to combine, then stir in buttermilk and yolks. Whisk eggwhite and a pinch of salt in a separate bowl until firm peaks form (1-2 minutes), fold half into corn mixture to lighten, then fold in remaining eggwhite.
Heat 3cm vegetable oil in a deep-sided frying pan over medium-high heat. Add heaped tablespoons of corn mixture to oil in batches and cook, turning once, until golden and puffed (3-4 minutes each side). Remove fritters with a slotted spoon and drain on absorbent paper. Season with sea salt and serve hot with lemon-paprika mayonnaise.