In a medium saucepan, melt the butter over medium-high heat until hot and foamy.
Add the shallots, and cook until soft and translucent, about 3 minutes.
Stir in the garlic and red pepper flakes, and cook until aromatic, about 30 seconds.
Add the wine, along with the tarragon sprigs.
Bring to a boil, then reduce the heat to medium, and simmer until the liquid has mostly reduced, about 7 minutes.
Remove and discard the tarragon sprigs.
Stir in the cream and return to a simmer.
Reduce the heat to low, cover slightly, and cook until thickened slightly, about 10 minutes.
Remove from the heat, stir in the lemon zest and juice, and season with salt and pepper.
Set aside, and keep warm.