Assemble all your ingredients along with a whisk or spatula. The first few steps of this recipe go by quickly.
Heat butter in a saucepan on medium, or medium low heat.
When the butter melts, add the flour and whisk immediately so the flour gets bubbly in the butter, and turns a light gold color. Be careful, the flour will brown quickly. If your butter is too hot, take it off the fire before adding the flour. Whisk and return it to the fire.
Next add the half and half in a steady stream while whisking with the other hand so that the half and half and flour combine into a smooth mixture.
Let this cook for a few minutes, make sure you stir every 10-15 seconds, until the sauce starts to bubble and thicken. Keep the heat at medium low. If it is too low, the sauce will not thicken. Don't crank it up too high, or the sauce will boil up too quickly and overflow. The sauce should begin to thicken in about 5-8 minutes. If it is taking too long, try raising the heat at bit. Or whisk in another 1/2 teaspoon of flour.
Once the sauce thickens and turns silky, lower the fire and add salt, pepper and other seasonings, stir a couple more times and cook for another 2 minutes. Taste and adjust the seasoning before turning off the stove.
Serve hot, tossed with pasta, and topped with fresh grated parmesan, and any protein and veggie on the side. The sauce will form a skin as it turns cold. Just whisk it again a couple times and it will be just fine.
