I grabbed this from one of my other posts 
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The next time you are feeling especially fresh on a HIT day try an escalating MPA pull-down effort using XMB. Warm up, go to Challenge Level 2 (CL2) on first few intervals. Then shoot for CL4, then CL6, and try to get all the way up to CL10 on a final “BT interval”.
Hold it there as long as you can.
On a Garmin you’ll earn a BT badge. On EBC Android you’ll go “deep purple”.
Shorten the recoveries while you do this. I.e. ignore the Recovery Timer and watch the CL gauge instead. Go again as soon as CL drops by two levels. For example, when you reach CL4 go again as soon as CL drops to 2. When you reach CL6 go again when CL drops to 4. Continue up the CL ladder as high as you can go and ride the last interval to failure.
If you have something left in the tank afterwards, try for another CL10 (multiple BTs).
On a Garmin you’ll see BT in 30 secs @ X watts pop up when you’re in proximity.
You can either hold watts close to target or raise the effort and shorten the time it takes to reach CL10.
I find the XMB method a fun way to go for it when my signature has gone stale. Or if I’m riding irregularly and decay has lowered my TP.
You won’t always achieve a BT if your signature is already dialed in.
Some days I’ll start off with good intentions, get to CL8, and realize “uh-uh, not today”. 
Back to your regularly scheduled programming to fill the buckets.