Put oven rack in middle position and preheat oven to 350°F. Generously butter a 9-inch square baking pan.
Toast oats in another baking pan, stirring occasionally, until pale golden, about 12 minutes.
Beat butter and sugar with an electric mixer until fluffy. Beat in eggs, milk, and vanilla. Whisk together flour, nutmeg, salt, and baking soda, then beat into butter mixture until incorporated. Stir in oats, pecans, and cranberries. Spread in buttered pan.
Bake until golden and a wooden pick inserted comes out clean, 30 to 35 minutes. Cool in pan 20 minutes, then cut into bars.
Makes 24 bars.