Spray a 7 inch x 4 inch pan with baking spray. Set aside.
Melt butter. Set aside.
In a small bowl, whisk together flour, milk powder, yeast, and salt. Set aside.
Combine sponge and water in the bowl of a stand mixer fitted with dough hook.
Turn on low speed to start.
Increase speed as needed to make a dough that is smooth, about 5 minutes.
Add yolks, one at a time, working back to a smooth dough after each. (Takes about 1 minute per yolk.)
Add sugar.
Knead until it is fully incorporated and dough is smooth, about 1-2 minutes.
Add liqueur and melted butter.
Knead until smooth, about 2-3 minutes.
Add flour mixture.
Knead on low until incorporated.
Increase speed to medium high.
Knead for an additional 5 minutes, or until dough is completely smooth and windowpanes when you stretch a small amount.
Add fruit.
Continue to knead on low speed until fruit is incorporated, 1-2 minutes.
Turn dough out onto a surface that has been lightly coated with water. (You could also use flour or cooking spray.)
Use a bench knife to round the dough, working until it is smooth on top.
Place in prepared pan.
Cover lightly with plastic wrap that has been sprayed with cooking spray and allow to rise in a warm spot (78℉) until dough crowns the edge of the pan, about 3-3½ hours. (You can also use a proofing box with a water tray set to 78℉. Leave dough uncovered if using proofing box.)
While dough is proofing, heat oven to 350℉.
Bake until dark brown, about 40-45 minutes. (Internal dough temp should be 190℉-195℉.)
Allow to cool in pan for about 10 minutes.
Remove from pan.
Place on cooling rack to finish cooling.