Use culinary-grade dried lavender to avoid any chemical residues. Do not use potpourri lavender.
If you don't have an ice cream maker, you can freeze the custard in a shallow metal pan, stirring every 30 minutes with a fork to break up ice crystals until frozen solid.
For a stronger lavender flavor, increase the lavender in the steeping milk slightly, but be careful not to make it soapy-tasting.
Store in an airtight container in the freezer for up to one month. Let sit at room temperature for 5 minutes before scooping for best texture.