Clean mussels thoroughly and place them in a saucepan with wine. Cover and bring to a simmer. With a spoon, rotate mussels in the wine. As the shells open, remove them from the saucepan and allow to cool. Discard any mussels that don’t open. To de-beard your mussels, pull the threads down towards the pointy end of the shell, discarding the brown foot and any muscle attached to the shell. Remove mussel meat from the shells, then remove tongues and the main (round) muscle. Cut mussels into halves or thirds depending on size. In a small bowl, mix mascarpone, lemon zest and juice together and set aside until required. Grate parmesan and chop onion. Put flour, salt, baking powder and pepper in a bowl and mix together. Add eggs and milk to create a thick batter, and then add parmesan, onion and mussel meat. Mix through the batter. In a non-stick pan, heat a splash of olive oil until hot and add a generous spoonful of batter for each fritter. Cook until golden brown on both sides and firm to the touch. Repeat until all the batter is cooked. Keep warm or reheat in a microwave before serving. If capers are salted, soak in water for about 10 minutes. Heat canola or vegetable oil until it shimmers and fry capers until crispy. Remove and drain on paper towels. Place fritters on a board draped with baking paper, and serve with a heaped tablespoonful of mascarpone and sprinkled with fried capers. Garnish with pea tendrils.