At this point I've posted about crumble so many times I initially was going to take a pass on posting yet another crumble picture. Because I made such a large one I used 4 Tablespoons of flour to thicken about 8 1/2 cups of fruit.
Hawthorne Valley Farms sells it at the Market, Saxelby and Whole Foods do as well. Quark is a thick sour cream like fresh fermented cheese similar to Formage Blanc. It gives whipped cream a luxurious thickness and a sour tang, so much so I added some sugar and a splash of vanilla. I didn't really measure what I was doing but an approximation would be 1/2 cup heavy cream , 1/4 cup Quark, 1 teaspoon Vanilla, 1 Tablespoon sugar and whisk! Because the Quark is so thick it takes no time to whisk it together, unlike heavy cream which can take several minutes to get the right thickness, this is almost instant.
Adjust to taste, thinning it with more cream if it's too thick or sour for you or adding more sugar or vanilla. I always like the contrast of thick, rich, slightly sour juxtaposed to a sweet buttery crumble so try not to over do the sugar! This is definitely a recipe to try, it would be awesome with chocolate cake.