I've never used lavender, but I'd be worried that (like a lot of aromatics) you might ruin it by boiling it. Then again, I don't know if that's the case for lavender. You might consider making a lavender "extract". Soak it in vodka to extract the aroma and flavor, and then use something like a graduated cylinder with an existing beer, adding small measured amounts at a time until you find the concentration you like.
Next: House ESB and Best Bitter
Primary: House Dark Mild
Souring: Brett C Old Ale, '15 Lambic, '14 Lambic, Flemish Red, Flemish Pale, Oud Bruin, Session Kriek
Bottled: Gose, Lichtenhainer, Gruit, Honey Porter, Kitchen Sink Tripel-ish-thing, Belgian Blond, Oat Dark Mild
Casked: House Ordinary Bitter
Kegged: Wheat Dark Mild, English IPA
Cellar: Brett B Tripel, '11 Lambic, Brett C Barleywine, Quad, Sour Stout, Brett C Bitter, Wild Cider, Wee Heavy, Brett B Red, Brett L Kriek, Bière de Garde