Irish whiskey butter: place 1/2 cup of room temperature unsalted butter in a mixing bowl and whip until fluffy. With mixer running, gradually add 3/4 cup powdered sugar. Slowly add 1/4 cup Irish whiskey until combined. Mixture may look separate and curdled at first, but if you keep whipping, it will come together. Use at room temperature or chilled.
Preheat oven to 365 degrees. Lightly grease 11x7" baking dish and set aside.
In a medium bowl, combine strawberries, rhubarb, sugar, cornstarch, and lemon juice. Toss to coat. Pour strawberry mixture into prepared baking dish.
In a medium bowl, add the flour, oats, light brown sugar, and salt, stirring to combine. Add the diced butter to the flour mixture, and using your fingers, work the mixture until it resembles coarse crumbs. Pour crumb mixture evenly over top of strawberry mixture.
Place baking dish in the oven and bake for 40 minutes, or until filling is bubbly and topping is golden brown.