To small saucepan, add honey, serrano pepper, red pepper flakes, and vinegar. Heat on medium-low for about 7 to 10 minutes, or until mixture starts to simmer. Remove from heat, add rosemary sprig, and allow it to infuse with peppers for a further 10 to 15 minutes. Strain through a fine mesh sieve into clean Mason jar, and reserve. Seal jar if making ahead of time.
