This is the classic filling for strudel and is easy to make. This version is adapted from Nick Malgieri’s instructions on Craftsy.
2 Tbs. unsalted butter
2-1/2 lbs. Granny Smith or Golden Delicious apples
2/3 cup sugar
1 tsp. cinnamon
½ cup dried currants or raisins
½ cup coarsely chopped walnuts
Peel and core the apples. Cut them into quarters, and then half each quarter lengthwise. Cut each of the 8 segments into 4 chunks.
Put the cut apples, sugar, cinnamon, and currants or raisins into a medium saucepan. Mix together. Nestle the butter in the middle of the apples at the bottom of the pan. Heat over medium heat until the apples start to sizzle. Cover the pan and reduce the heat to low. Cook 10-20 minutes until the apples have exuded a large amount of water. Remove the lid and cook, stirring occasionally, until the most of the liquid has evaporated. Cool the filling to room temperature before using. Use when cool or store overnight in the refrigerator.
Just before filling the strudel, stir in the walnuts.