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.
Fermenting: Gruit, Honey Porter
Souring/Funkifying: Brett C Old Ale, Lamebic '15, Lamebic '14, Flanders Red, Flanders Pale, Oud Bruin, Session Kriek
Bottled: APA, American Amber, Robust Porter, Gose, Lichtenhainer, Petite Saison, Saison, Mixed Berry Peppercorn Hydromel, Irish Red, Pale Mild, Dry Stout
Bottle Cellar: Brett B Tripel, Brett C Barleywine, Lamebic '11, Quad, Tripel, Brett C Bitter, Wild Cider, Sour Stout, Wee Heavy, 100% Brett B. Red, 100% Brett L. Kriek