Using half spelt or whole wheat gives the dough a light tan color. It also absorbs more liquid than white flour, so you'll need to use more cold water to make it come together. A rest of at least 30 minutes in the fridge lets the butter cool off, and also lets the flour absorb and distribute the moisture, making it easier to roll out. I use a food processor to make pie dough quickly.
In the food processor, place the flours, salt, and butter. You can also do this by hand if you like. Pulse and process until the butter is cut in, so pieces about the size of peas are still visible.
Add about half the water, and pulse a few time (or mix by hand). Continue to add more water a few tablespoons at a time until the dough becomes crumbly and will hold together when pressed.
Dump out onto a floured counter, and press/knead/roll the dough until it comes together into one piece. I like to make a loose log, then cut it in half.
Using two pieces o was paper, make a disc of dough, wrapped up in the plastic, and refrigerate at least 30 minutes before using.