Four botanicals and one order of operations. The fennel simmers for three minutes, because the anethole that makes it taste sweet comes out in heat; then the heat goes off and the chamomile, lavender, valerian and a couple of mint leaves steep, covered, for six or seven minutes. That sequence is not fussiness. The European Medicines Agency's template for telling patients how to prepare a herbal tea has a line saying aromatic herbs like mint may be infused at the end of a decoction, and that line describes this cup exactly. What you get is honeyed and floral on top, with the valerian root underneath, and the recipe adds no sugar.
The evidence is narrower than the name. Chamomile's clinical reputation rests on capsule extracts: the one dedicated trial in chronic insomnia gave 34 adults a standardised extract for four weeks and found no difference from placebo, and its authors calculated that the dose stood for 15 grams of flowers a day, more than any teapot delivers. The trial that used tea, 80 women with poor sleep after childbirth, improved sleep and mood at two weeks and showed no difference by four. Pooled across twelve trials, chamomile improved sleep quality and did nothing for state anxiety. Lavender's strongest result belongs to a licensed oral preparation, not to petals in hot water. The Journal's notes on chamomile and on herbs for chronic stress walk through all of it.
So drink it for what it is: a warm, sweet, sedative-leaning cup that ends the day, taken covered so the lavender's linalool stays in the water rather than the kitchen air, just before bed. Keep the valerian at the small amount the recipe gives; it is the sedative in the cup.