In a measuring cup or small bowl, mix together milk and lemon juice. Let stand while you prepare the rest of the ingredients.
In a large bowl, combine flour, salt, baking powder and sugar. Add cold butter and cut in with a pastry blender until butter is the size of peas. Add cheese and mix.
Add milk to dry ingredients. Mix just until it comes together. Then turn out onto a floured counter top. Knead 2-3 times just to combine and press out until dough is about 1 inch thick. DO NOT OVER WORK THE DOUGH!
Cut Biscuits with a 3 inch biscuit cutter. Press straight down, do not twist or biscuits will not rise. Place onto un-greased cookie sheet so sides are just touching.
Beat egg with 1 tsp milk and brush on top of biscuits.
Bake on center rack of oven for approximately 22 minutes.