Spread the oats out on a baking sheet and toast until they smell nutty, 8-10 minutes. Add the oats, flour, ½ cup brown sugar, cinnamon and salt to a food processor and process until blended. While the machine is running, pour in the melted butter and continue to process until the mixture clumps.
Press the oat mixture into the bottom and up the sides of a 9-inch springform pan then bake the crust 10-12 minutes, or until firm. Remove the crust and let cool to room temperature.
Reduce the oven to 325.
Wrap the base of the springform pan in aluminum foil and place it in a roasting pan.
To make the filling, beat the cream cheese, granulated sugar and remaining ½ cup of brown sugar at medium speed until smooth. Continue beating and add in the Irish cream and heavy cream.
Add each egg separately, gently beating each with a fork to loosen the yolk first before adding it in. Mix to incorporate before adding the next one.
Pour the filling into the springform pan, then pour boiling water into the roasting pan so it reaches 1 inch up the side of the pan.
Bake the cheesecake until the edges are set but the center still jiggles, approximately 1 hour.
Turn off the oven but leave the cheesecake inside for one hour more. Do not open the oven (though how you're supposed to check to see if the center still jiggles without doing that, I don't know).
After the hour, let the cheesecake cool to room temperature on the counter, then cover with plastic wrap and chill for 3-24 hours. Top cheesecake with whipped cream and chocolate shavings if desired.
Notes
What I'd Do Different Next Time
I'd go with a different crust, maybe one with Biscoff cookies as the main ingredient.