Preheat oven to 350°F and grease or line a 12-cup muffin tin.
In a large bowl, beat butter with brown sugar, granulated sugar, coffee, and vanilla until light and fluffy.
Beat in eggs, then milk, mixing until smooth.
In a separate bowl, whisk together flour, salt, and baking powder.
Alternately add dry ingredients to the butter mixture, stirring just until combined.
Fold in the good stuff: Gently fold in chocolate chips and walnuts.
Fill muffin cups: Divide batter evenly between 12 muffin wells, filling them nearly full.
Bake for 20–25 minutes, until a toothpick inserted comes out clean.
Cool & enjoy! I love these served warm with a pat of butter.