First, preheat a large skillet over medium heat, and add the butter. Let it melt; lower the heat if it sizzles too much.
Meanwhile, whisk together the milk, eggs, sugar and Irish Cream Liqueur. Dunk each bread slice in the mixture for about 5 seconds per side, and then place in the skillet.
Cook each bread slice for about 3-4 minutes, until golden brown on each side.
While the French toast cooks, make the Irish Cream sauce by whisking together all of the ingredients until smooth. Taste and adjust with more powdered sugar, if necessary.
Serve two slices of French toast on each plate, top with an extra pat of butter, and drizzle with Irish Cream Sauce.