Preheat oven to 325°F (170°C). Spray a light-colored metal 8½x 4½-inch loaf pan with cooking spray. Line pan with parchment paper, letting excess extend over sides of pan.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and sugars at medium-low speed just until combined. Increase mixer speed to medium, and beat until fluffy, 3 to 4 minutes, stopping to scrape sides of bowl. Add eggs and egg yolk, one at a time, beating well after each addition. Beat in vanilla.
In a medium bowl, whisk together flour, salt, and baking powder. In a small bowl, whisk together sour cream, liqueur, and 1½ tablespoons (22.5 grams) water. With mixer on low speed, gradually add flour mixture to butter mixture alternately with sour cream mixture, beginning and ending with flour mixture, beating just until combined after each addition and stopping to scrape sides of bowl. Fold in chocolate. Spoon batter into prepared pan; using a small offset spatula, spread into an even layer.
Bake for 50 minutes. Rotate pan, and bake until a wooden pick inserted in center comes out clean and an instant-read thermometer registers 200°F (93°C) to 205°F (96°C), 25 to 30 minutes more, loosely covering with foil during final 15 minutes of baking to prevent excess browning. Let cool in pan for 10 minutes. Using excess parchment as handles, remove from pan, and let cool completely on a wire rack. Spoon and spread Irish Cream Glaze onto cooled cake as desired before serving.
Recipe by Bake from Scratch at https://bakefromscratch.com/irish-cream-loaf-cake/