Snap off tough ends of asparagus. Cook asparagus, covered, in a small amount of boiling water for 6 to 8 minutes or until crisp-tender. Drain. Arrange asparagus spears in serving dish and keep warm.
Melt butter in a small saucepan over low heat. Gradually stir in chicken broth and half-and-half. Cook, stirring constantly, until thickened and bubbly, about 1 minute. Whisk in mustard, lemon juice, and pepper. Spoon sauce over asparagus. Serve immediately.