This is safe according to Cooks Illustrated (published by America's Test Kitchen who I trust implicitly when it comes to food).
This process takes at least THREE WEEKS to complete, so make sure you have time to let it age.
The alcohol will actually kill any bacteria/salmonella that may be in the eggs (highly unlikely anyway) but the three weeks is the time it takes. Rockefeller University did a study where they purposely infected the product with salmonella and after three weeks it was all dead.
The secret is not to add the dairy until you are ready to serve.
1 1/2 oz 80 proof liquor per egg
1 dozen Eggs
1 1/2 cup Bourbon
1/2 cup Cognac
1/3 cup Dark Rum
1 1/2 cup sugar
6 cups whole milk
1/2 cup heavy cream