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: Wheat Mild, English IPA
Primary: WGV Bitter
Souring: Brett C Old Ale, '15 Lambic, '14 Lambic, Flanders Red, Flemish Pale, Oud Bruin, Kriek
Bottled: Gose, Lichtenhainer, Irish Red, Dry Stout, Gruit, Porter, Wit, Tripel, Blond
Casked: Pale Mild, Oat Mild, BX Bitter
Cellar: '10 Brett B Tripel, '11 Lambic, '13 Brett C Barleywine, '13 Quad, '13 Sour Stout, '14 Brett C Bitter, '14 Wild Cider, '15 Wee Heavy, '15 Brett B Red, '15 Brett L Kriek, '15 Bière de Garde