What starts with t and ends with t and has t in the middle?

Depends on how strictly you define "the middle," I guess. But there are plenty to choose from here:

tantamount

tarantist

tartest

tartiest

tartlet

tastiest

tautest

teentsiest

teetotalist

teletext

tentiest

teratologist

territorialist

testament

testiest

tetchiest

tetravalent

thanatologist

thatchiest

thaumaturgist

thermostat

thirstiest

thistliest

thriftiest

throatiest

tightest

tightknit

titbit

titlist

titrant

titubant

toastiest

tomtit

toothiest

toothwort

toploftiest

totalist

totemist

totipotent

traditionalist

transductant

treatment

tritest

tritheist

trothplight

troutiest

trustiest

tuftiest

twistiest

twitchiest

tzitzit