In a bowl, whisk cream with yogourt, sugar and 2 tbsp (30 mL) lemon juice until sugar dissolves. Cover loosely with a kitchen towel. Leave at room temperature until thickened, 1 to 2 days. Then line a sieve with a cheesecloth folded into 6 layers. Place over a bowl and pour in thickened cream. Refrigerate until most of excess liquid is drained off and mixture is very thick, about 4 hours. Once thickened and strained, cover and refrigerate up to 1 week.