How to turn teosinte into corn?
Initially I didn't like this question very much, but I changed my mind when I realized that there is actually ongoing research to do exactly what you propose in order to study just how long it takes to get maize from teosinte.
John Doebley at the University of Wisconsin-Madison has a project ongoing to breed 30 generations of teosinte to be more &quot;corn-like&quot; on a single parameter, the length of the lateral branches.
The first challenge is to find a strain that isn't already contaminated by modern maize - that isn't completely possible, but he selected a strain that has minimal hybridization. You would have to do the same.
Second, you have to plant someplace isolated to further prevent hybridization. Dr. Doebley has a plot in Hawaii for this purpose.
Note that even though this scientist is only selecting over 30 generations, he doesn't anticipate that much of a change (i.e., he doesn't expect to have anything like corn when he is finished), and he is only selecting on a single parameter and furthermore, this parameter was chosen specifically for being easy to score, showing a lot of variation in the existing population, and influenced by a known single gene. Many more generations would be expected to get a product like modern corn. And even domesticated corn has changed significantly over thousands of years of agriculture.
For this answer, I simply reference the project site that I linked above, but in case that link goes dead, here is some literature that the project cited directly:

Beadle, G. W., 1977  The origin of Zea mays, pp. 615-635 in Origins of Agriculture, edited by C. E. Reed. Mouton, The Hague.
Beadle, G. W., 1978  Teosinte and the origin of maize, pp. 113-128 in Maize Breeding and Genetics, edited by D. B. Walden. John Wiley &amp; Sons, New York, NY.
Doebley, J., A. Stec and C. Gustus, 1995  teosinte branched1 and the origin of maize: evidence for epistasis and the evolution of dominance. Genetics 141: 333-346.
Doebley, J., A. Stec and L. Hubbard, 1997  The evolution of apical dominance in maize. Nature 386: 485-488.
Doebley, J. F., A. Stec, J. Wendel and M. Edwards, 1990  Genetic and morphological analysis of a maize-teosinte F2 population: implications for the origin of maize. Proc. Natl. Acad. Sci. 87: 9888-9892.
Iltis, H., 1987  Maize evolution and agricultural origins, pp. 195-213 in Grass systematics and evolution, edited by T. Soderstrom, K. Hilu, C. Campbell, and M. Barkworth. Smithsonian Inst. Press, Washington, D. C.
Wang, R.-L., A. Stec, J. Hey, L. Lukens and J. Doebley, 1999  The limits of selection during maize domestication. Nature 398: 236-239.
Wilkes, H. G., 1967  Teosinte: the closest relative of maize. The Bussey Institute, Harvard University, Cambridge.
Wilkes, H. G., 1977  Hybridization of maize and teosinte in Mexico and Guatemala and the improvement of maize. Econ. Bot. 31: 254-293.