Here's my recipe from last year:
Derby Day Ale- Mint Julep
3.50 American Six-row Pale
3.00 Flaked Corn
0.25 Black Patent
0.50 American Crystal 120L
1.00 Flaked Rye
3.00 Light Malt Extract Syrup
1 oz Perle hops
(0.5 oz @ 60min, 0.5 oz @ 5 min I think is what I did)
I bottled 2 gallons of the beer as is, then took three gallons and turned mint julep-ized it. (Ya, julep is a verb now)
Soak 1 oz mint in 12 oz vodka for 12 hours. Replace with fresh mint for 12 hours, repeat once more for 12 hours. (using 3 oz mint total)
Add mint extract, ~12 oz bourbon, and a pinch of champagne yeast at bottling.
When brewing this again I will soak the mint in bourbon, and omit the vodka.
I'm brewing it again this year but may use cornmeal or grits in place of the flaked corn.