Combine the buttermilk, onion, oregano, paprika and garlic in a medium-sized bowl. Add the chicken pieces, cover with plastic wrap and refrigerate overnight.
Remove the chicken from the buttermilk and drain in a colander. Strain the buttermilk into a medium-sized bowl, discarding the solids. Combine the spice-coating ingredients in a large zip-lock bag. Add the chicken pieces, a few at a time, and shake to coat. Dip the chicken in the reserved buttermilk and coat again in the spiced flour. Arrange on a wire rack and set aside for 15 minutes, to dry slightly.
Meanwhile make the mayonnaise: whisk the egg yolks, mustard and lime juice together in a small bowl. Gradually pour in the oil, whisking continuously, until thick. Add the chipotle and adobo purée and stir to combine. Season with sea salt. Transfer to a small serving bowl, cover and refrigerate.
Fill a deep-fryer or a large heavy-based saucepan two-thirds full with vegetable oil and heat to 190°C (375°F). Place a clean wire rack on a baking tray, for draining. Cook the chicken in batches for 8–10 minutes, until crisp, golden brown and the juices run clear when a skewer is inserted into the thickest part of the flesh. Drain on the rack. Serve hot with chipotle mayonnaise and lime wedges.
This recipe is excerpted with permission from <a href="http://www.amazon.com/gp/product/1742704514/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1742704514&linkCode=as2&tag=craftfocom-20">"Great Pub Food: Make Home Your New Local"</a> by Rachael Lane and published by Hardie Grant Books.