Combine all salsa ingredients in a small bowl, set aside.
Roughly chop corn kernels. Whisk egg white until stiff.
Combine polenta, flour, salt, and bicarb in a mixing bowl. Make a well in the centre, add butter, buttermilk and egg yolk. Stir until just combined. Fold through corn and shallots, then egg white.
Heat a little oil in a large non stick frypan. Over a medium heat, cook 1/3 cup measures of the batter for 2 minutes or until bubbles form on the surface, turn and cook for a further 2 minutes. Keep corncakes warm, repeat with remaining batter.
Serve corncakes stacked with roasted tomatoes and yellow papaw salsa.