For the ice cream, heat both milks and salt until starts to simmer in a 3 quart pot. Whisk sugar with eggs and egg yolk until it gets thick. When milk is ready, slowly pour mixture into egg mixture whisking slowly to incorporate. Whisk well, then slowly pour mixture back into pot. Stir mixture on medium heat until mixture reaches 170 degree or until mixture thickens and coast back of spoon or spatula. Do not bring to boil. With a strainer over a clean bowl, pour mixture. Whisk in zest, vanilla, and elderflower syrup. Cool down mixture by stirring every few minutes and place bowl in a large bowl filled with ice water. Let the mixture stay chilled in the refridgerator for at least 12 hours or overnight.
For Rhubarb Compote. Place rhubarb, sugar, orange juice elderflower, salt ,vanilla bean paste in large 3 quart pot. Stirring frequently bring to a boil and then turn heat down and simmer until liquid is reduced by half. Mixture will be thick and sryupy and delicious. Pour mixture into clean bowl and cool down.
To make ice cream ,freeze in your ice cream maker according to its directions. I have plastic pint containers I put my ice cream in. When ice cream is churned and ready to pint up I alternate between ice cream and rhubarb compote. When container is full take knife and swirl mixture together. Freeze in freezer and enjoy