Combine all dry ingredients, plus a pinch of salt, in a bowl; set aside. Mix egg yolks with buttermilk and oil. Incorporate yolk mixture into dry ingredients. Whip egg whites to medium peaks with whisk or hand mixer and fold into batter in 3 stages to incorporate fully (and to make fluffier waffles). Ladle 1/4 batter onto a nonstick waffle iron until griddle is covered but not overflowing (waffle iron sizes vary; adjust if necessary). Cook waffles until golden, 3 to 4 minutes; keep warm in oven. Repeat 3 times. Optional sauce: Bring honey and lavender to a simmer in a small pot. Take off heat, cover and let steep 30 minutes. Strain honey into a jar and discard lavender.