Mix the tahini and honey together. Spread the mixture on a slice of bread (sourdough works well for toasting). Scatter over the feta and a few thyme leaves, then top with another slice of bread. Butter the outsides and press sesame seeds into each side. Fry in a hot pan, weighed down by another pan, for 2 mins on each side (or use a toasted sandwich maker), then drizzle with honey.