In a medium saucepan, cook leeks with 1 tablespoon of butter over medium flame until translucent; do not brown. Next, scald milk (do not boil); stir in the butter, leeks, sweet corn, roasted garlic, fresh thyme, cornmeal, and salt. Cook, stirring constantly, until cornmeal comes away from sides of pan and thickens. Set aside to cool until lukewarm.
Add beaten egg yolks; mix thoroughly. Fold in stiffly beaten egg whites; mix gently but thoroughly. Pour into greased 2-quart baking dish. Bake at 375°F for one hour or until top is golden brown.
While spoonbread is in oven, place 2 tablespoon of olive oil in a medium saucepan, and heat over a medium flame. Next, add minced garlic and cook until golden brown. Add diced tomatoes, basil, lemon zest, and salt. Cook tomatoes for about 3 minutes.
Serve spoonbread hot out of the oven with tomatoes spooned over the top.