How to Make It
Heat a large, high-sided skillet over medium-high. Add beef fat, and heat until shimmering, about 2 minutes. Add haricots verts, and cook, stirring often, until bright green, about 4 minutes. Add hazelnuts, garlic, and butter, and cook, stirring often, until hazelnuts are toasted and haricots verts are crisp-tender, 4 to 6 minutes. Remove from heat; stir in lemon juice, tarragon, salt, and black pepper. Serve immediately.
To make 1/2 cup of rendered beef fat, gently heat 8 ounces of beef trimmings in a small saucepan over medium-low for 1 hour. Strain the rendered fat before using.