ah ok
well
then light two fuses, though one from both edges.
When the first one is all burnt, 1/2 hour has elapsed, so light the other edge of the second fuse which has half the time left. When you burn from both edges you reduce the time half the time, and since half the time of half the time=1/4 hour and as 1/4h+1/2h=3/4h=45minutes, you've managed the measuring.
45 minute problem solved.