Place nuts in a food processor and grind until finely ground.
In a bowl beat 1/2 cup of sugar and 1/4 cup of the butter until blended. Add the egg yolks, one at a time, beating well after each addition. Mix in the ground nuts, lemon juice, lemon peel and all but 2 tablespoons of the flour.
In a deep bowl beat egg whites with a mixer on high speed until soft peeks form. Gradually beat in 1/4 cup sugar until the whites hold stiff, shiny peaks. Gently fold the whites into the yolk mixture.
Spoon the batter into a buttered and floured 9-inch cheesecake pan with removable rim. Bake in a 350 degree oven until the torte is very lightly browned and the center feels just barely firm to the touch, about 20 to 25 minutes.
To prepare the topping, in a medium sized pot melt remaining 1/2 cup butter over a medium heat. Add the remaining sugar, flour and nuts. Stir the mixture until bubbling. Immediately spoon the toffee topping evenly over hot torte, pushing nuts with a spoon to arrange decoratively. Return to oven and bake until nuts and topping are slightly more brown, about 15 to 20 minutes longer.
Cool torte in the pan for 10 minutes, then run a knife inside the pan rim to release. Remove pan rim. Serve torte warm or cool.
TIP: PAN ROASTING ALMONDS
Spread shelled nuts in a single layer on a baking pan. Bake in a 350 degree oven, stirring often, until golden, about 15 minutes.