In a saucepan, combine lemon zest, lavender, milk, and cream. Bring to a boil. Steep for 20 minutes. Strain. Whisk the egg yolks and sugar together. Whisk 1 cup of the hot cream into the egg mixture. Mix thoroughly. In a steady stream, slowly add the egg mixture to the hot cream mixture. Continue to cook for 4 minutes, stirring occasionally. Remove from the heat and cool completely. Strain the mixture. Add the mixture to the electric ice cream maker. Process according to manufacturers' directions.