Step 1Heat the oven to 350 degrees. Melt the butter in a saucepan. Add the flour and stir over low heat. Add the milk all at once and whisk over moderate heat, bringing to a simmer, until the bechamel thickens and is smooth without lumps.
Step 2Crumble the Gorgonzola into the warm bechamel, stir to combine, and season to taste with salt and pepper. Allow the mixture to cool, then add the egg yolks.
Step 3In a separate bowl, beat the egg whites to stiff peaks. Fold them into the cheese bechamel.
Step 4Butter 8 (4-ounce) ramekins well on all sides and fill them to just under the brim. Place the sformatini in a baking dish and pour in enough warm water to fill the dish halfway. Bake for 1 hour or until the tops are gently browned and a probe comes out clean.
Step 5While the sformatini are cooking, cut the tomatoes into a small, coarse dice. Place them in a pan and cook them quickly on high heat, only to soften them, about 2 minutes. Pass them immediately through the fine plate of a food mill to create a smooth and pourable puree. Season to taste with salt and pepper.
Step 6Mix the potato starch with a little cold water (about 1 tablespoon) to make a thin slurry and whisk it into the hot tomato sauce. This will keep the tomato's liquid and pulp in emulsion and prevent it from separating at its pooled edges.
Step 7Remove the ramekins from the oven and allow to cool slightly. Run the edge of a sharp paring knife around the sides of the puddings. Holding each ramekin in one hand, carefully turn the sformatino out onto your other hand, and then place it browned-side-up on a warm plate. Spoon a little sauce around each portion.