Start by placing a sugar cube on a napkin. 

Dash the sugar cube with Angostura bitters. Give it a minute to soak through.

Put the sugar cube in the glass and add club soda. Stir well or use a small mortar to dissolve the sugar completely. It's important that there are no sugar lumps.

Add ice cubes and half of your bourbon. 

Stir for 1-2 minutes to combine everything.

While stirring, add more ice and bourbon until you are satisfied with the taste. 

When satisfied, add more ice - the temperature should be low.

Cut a slice of orange peel and run its outside around the rim of the glass (optionally burn it briefly).

Twist it and drop it into the glass.

Serve immediately.