Combine flour and next 6 ingredients in large bowl. Whisk eggs and broth in small bowl to blend. Gradually stir egg mixture into dry ingredients (batter will be loose).
Meanwhile, bring large pot of lightly salted water to boil. Reduce heat to medium. Place rimmed baking sheet close by.
Working with 1/2 cup batter at a time and using flexible rubber spatula, press spaetzle batter through 1/4-inch-wide holes of spaetzle maker or colander. Boil until tender, about 3 minutes. Using skimmer, lift spaetzle from pot. Drain; place on baking sheet.
Melt butter in large skillet over medium-high heat. Cook until butter browns, stirring occasionally, about 4 minutes. Add spaetzle; sauté until beginning to brown, about 4 minutes. Add spinach and radicchio; toss until wilted, about 3 minutes. Squeeze some lemon juice over spaetzle. Season with salt and pepper.
