Combine whole wheat flour, undissolved yeast, sugar and salt in a large bowl. Heat milk, water and butter until very warm (120° to 130°F). Add to flour mixture. Beat 2 minutes at medium speed of electric mixer, scraping bowl occasionally. Add 1/4 cup all -purpose flour; beat 2 minutes at high speed. Stir in enough remaining all-purpose flour to make soft dough. Knead on lightly floured surface until smooth and elastic, about 8 to 10 minutes. Cover; let rest 10 minutes.
Divide dough into 12 equal pieces; shape into balls. Place in greased 8 or 9-inch square pan. Cover; let rise in warm, draft-free place until doubled in size, about 30 minutes.
Bake in preheated 375°F oven for 15 to 20 minutes or until done. Remove from pan; cool on wire rack.
To make sliders, line a baking sheet with aluminum foil. Spray with cooking spray. Divide ground beef in half. Press one portion into a 9 x 6-inch rectangle on prepared baking sheet. Cut rectangle in half lengthwise. Now cut in thirds crosswise to make six equal sized square burgers. Repeat with remaining ground beef. Season as desired.
Grill over Medium Direct heat for 10 to 12 minutes, turning once. Center of burger should be 160°F with no pink remaining. OR, broil 7 to 9 minutes about 6 inches from heat, turning once. Slice dinner rolls and top with a Slider. Add burger toppings as desired.