Combine the flours, salt, sugar and butter in a food processor. Pulse a few times until the butter is combined and the mixture becomes crumbly in texture.

Beat the egg and milk together.

With the processor running, slowly pour in the egg and milk mixture until the dough comes together in a ball.

Turn dough out onto a floured surface, shape into a disk and wrap with plastic wrap.

Refrigerate the dough for at least an hour, up to overnight.

Place the oil and butter in a large skillet over medium heat.

Once melted, add the onion, mushrooms and beets. Toss once and then let the mixture cook, untouched for about 10 minutes until the mushrooms have released all their moisture and the mixture is starting to brown.

Add the chives to the skillet and toss to combine.

Pour the sherry vinegar in and stir, scraping up any brown bits stuck to the bottom of the pan.

Once liquid has cooked off, season with salt and pepper to taste and turn off heat.

Remove the dough from the refrigerator and let sit at room temperature for 30 minutes.

Preheat the oven to 375 degrees.

Roll the dough out into a circle on parchment paper.

Spoon the filling onto the dough leaving about a 1 inch border.

Sprinkle the blue cheese on top of the filling.

Gently fold up the sides of the dough in an overlapping pattern and press firmly to seal any creases.

Transfer the galette on the parchment paper to a baking sheet or pizza stone and bake for 40-45 minutes until the crust is golden brown.

Remove from the oven and let sit for 10 minutes before slicing.