Adapted from
Imbibe
I made a batch of Torontos and put them in a little aging bottle, which is kind of fun to experiment with. Any bitters that you like would work, such as orange, cardamom, Angostura, or another favorite.
To make simple syrup, boil together equal parts sugar and water, stirring, until the sugar is completely dissolved. Let cool to room temperature. You can use 1/4 cup (60ml) water to 1/4 cup (50g) sugar or increase it, if you plan to make more. Any extra can be kept in the refrigerator for a few weeks.