Melt butter in a pan, and add chopped bacon. When the bacon is browned; add risotto rice (arborio or carnaroli), and fry until just starting to brown.
Deglaze the pan with a couple of glugs of vermouth; then add finely diced onion and saute until translucent.
If there is still fond on the pan (uh.. brown bits), use some chicken stock to deglaze further. Then, add enough chicken stock to just cover the rice.
When the stock has evaporated off; cover the rice with stock again.
This time, when the stock evaporates, add sliced mushrooms; and again, cover the rice with stock.
When the stock evaporates this time; the risotto is probably ready. Sample a grain of rice, and if it tastes about right; stir in grated parmesan cheese and serve. Otherwise, continue adding and cooking off more stock until it’s finished.