[Darren Abbey]

Tiny Tim has two recessive dwarfing genes. In your hypothetical cross it is convenient to use the TT plant as the mother, as any selfed seeds will be tiny and any F1s will grow huge(normal) sized plants. Isolate this plant from others and save every seed it produces.

In the F2 generation, 1/16 of the plants will be micro (having two dwarfing genes in the homozygous state) and 6/16 of the plants will be dwarf (having one or the other dwarfing genes in the homozygous state). You can identify which plants are normal/dwarf/micro in the seedling stage with some practice, so you don't even have to grow them to full size. You can screen through many seeds and only grow the size you want.

Don't even bother to grow out F3s unless you saved seeds from a dwarf/micro F2. If the F2 you save seeds from is normal sized, it could have one copy of both, one, or neither of the dwarfing genes. If you luck out and it carries one copy of -both- dwarfing genes, then the seeds produced will have the same pattern of dwarfing genetics as the F2 seeds and you haven't gained anything. If neither gene is present, then you won't find any dwarf/micro plants in the next generation.
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Back-crossing to the larger-fruited parent variety is a good idea once you've recovered a dwarf/micro. It will increase the odds of having large-fruit genes. If you back-cross before you've recovered the dwarf/micro growth habit, then you will just be diluting the growth form genes and reduce the probability of finding them later.