What cocktails can I make with bourbon and Cointreau?

The Brown Derby (bourbon, grapefruit, honey) and the Bourbon Sidecar (bourbon, Cointreau, lemon) both work. Bourbon also subs into a Sidecar template cleanly.

Bourbon and Cointreau are not a classic pairing, but the combination is well-behaved if you bridge them with citrus. Two strong options: (1) Bourbon Sidecar — 2 oz bourbon, 0.75 oz Cointreau, 0.75 oz fresh lemon juice, shaken hard, served up with a sugared rim. The bourbon-Cointreau-lemon shape is the Sidecar template; cognac is the canonical spirit but bourbon works, just sweeter. (2) Brown Derby (with Cointreau as a Honey substitute boost) — 2 oz bourbon, 1 oz fresh grapefruit juice, 0.5 oz Cointreau, 0.25 oz honey syrup, shaken. Both drinks hit the citrus-sweet-spirit balance bourbon and Cointreau need. Skip the Old Fashioned and Manhattan when you have Cointreau — those drinks want sweet vermouth or sugar, not orange liqueur. The Cointreau is also great as a 0.25 oz float on top of a Whiskey Sour for additional aromatic complexity.