Step 1

Preheat oven to 400°F. Combine first 6 ingredients in processor and blend. Add butter and cut in, using on/off turns, until fine meal forms. Transfer to large bowl. Mix in cheese. (Can be prepared 4 hours ahead. Cover and chill.)

Step 2

Mix enough buttermilk into flour mixture to bind dough. Turn out onto floured surface and knead gently until combined, about 10 turns. Pat out dough to 3/4-inch thickness. Using 3-inch-diameter cookie cutter, cut out biscuits. Gather scraps, pat out to 3/4-inch thickness and cut additional biscuits. Transfer biscuits to ungreased cookie sheet. Brush biscuits with egg glaze and sprinkle with poppy seeds. Bake until golden brown and firm to touch, about 18 minutes. Serve warm.