Place tomatoes in a small Dutch oven; cook, uncovered, over medium heat until tender. Add soda, stirring well. Strain tomato mixture through a fine-meshed sieve, mashing pulp with back of a spoon; discard the pulp.
Return strained tomato mixture to Dutch oven; add milk, butter, salt, pepper, and cracker crumbs, if desired. Cook over medium heat, stirring occasionally, until thoroughly heated.
Ladle into individual serving bowls. Serve warm.