Looks like it could be Phacelia tenacetifolia.
Verbena bonariensis, butterflies love it too. We have some growing in our garden, it reseeds itself every year, we bought one plant 5 years ago and it keeps coming back every year. The buckeye butterflies really like it. WVMJ
Meadmaking with WVMJ at Meads and Elderberry Winemaking