I don't know too much about irish whiskey, but I recently researched how to make bourbon at home. I won't go into how you got the alcohol, in this case I was going to use 100 proof Stolichnaya.
What gives the bourbon flavor is charred virgin white oak. Virgin, i.e. the oak has never been used for anything else (port, sherry, etc.). You can use a cask, but I will use oak cubes. Use american white oak or spanish white oak, nothing else.
You can char the cubes by any method. But most people have a grill and that tends to be easiest way. You are looking for a brown/almost black charring, if it starts blacken to the point of burning, just scrape the worst of the black char afterwords. The entire point of charring is to carmelize the sugars present in the oak.
Fill a container with the now charred cubes and pour your alcohol of choice into the container. Seal and forget about it for 9+ months. It is supposedly going to come out very flavored even after 6 months, the theory is that there is more surface area with cubes than a cask. I haven't tried this yet, so take it with a grain of salt.
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