Season Salmon on both sides with salt & pepper. In a non stick pan on med/high heat add one tablespoon of olive oil and sear Salmon top side down until lightly brown. Take Salmon out of pan and place on a dish and set aside. Then in the same pan lower heat to low/med and add the other Tablespoon of olive oil and sweat diced onions with a dash of salt until translucent. Then dust the pan with flour to coat onions and cook for about a minute to take out the flour taste...then raise heat slightly higher and add one cup of champagne and let simmer and then swirl in heavy cream about a 1/2 cup and simmer until reduced and thickened (if the sauce gets too thick you can add some more champagne or some chicken stock to thin out sauce) and then add Salmon back to the pan and lower heat add cherry tomatoes and cook until Salmon is done. Time depends on how you like your Salmon. Add chopped tarragon at the very end.