Remove leaves from broccoli and cut off tough lower ends of stalks.
Peel skin from lower portion of stalks.
For even cooking, split each stalk in half, to 1" from floweret.
Arrange stalks in cooking bag suitable for microwave ovens.
Tie bag loosely with string, leaving space for steam to escape.
(Do not use metal twist ties.) Microwave at high setting 6 minutes.
Turn bag over.
Microwave at high setting 4 minutes more, or until tender-crisp.
Remove from bag and place in serving dish.
Top with butter and season with salt and pepper.
Garnish with lemon slices.