n. — Food, Prairies, especially Saskatchewan
a dessert square consisting of an oatmeal or pastry base, date filling and crumble topping.
Type: 1. Origin — Outside of the Prairies, a matrimonial cake is usually called a date square. The term appears to have originated in Canada, and is most frequent in Canada (see Chart 1), where Saskatchewan (see Chart 2) stands out, though it can be considered a Prairie term since Albert and Manitoba also show sizeable frequencies.
See also COD-2, s.v. "matrimonial cake", which is marked "Cdn (Prairies)", and OED-3, s.v. "matrimonial cake", which is marked "Canad.".
- 1928  MATRIMONIAL CAKE - Half lb. Butter, 1 cup Sugar, 2 cups Flour, 3 cups Rolled Oats, 1 tspn Soda. Mix into crumbs. Filling: 1 lb Dates, 1 cup Sugar, 1 cup Water. 
- 1941  Matrimonial Cake 1ΒΌ cups of rolled oats [...]. 
- 1951  But the name was a misnomer, I'm afraid, for it ne'er brought me a husband. Before he appeared on the horizon I had gone on to other recipes. A good thing perhaps, for if he had tasted my Matrimonial cake I might never have known whether he loved me for myself alone. 
- 1977  Elizabeth brushes the crumbs from her lap, from her comfortable tweed skirt, and rises to go out. Matrimonial cake is always so messy. Elizabeth Brewster in sensible shoes, covers the sidewalks in Saskatoon. 
- 1980  But as my mother did, I'm sure they must all have avoided juices and salads, loved pies and matrimonial cake, and great overdone roasts. 
- 2000  The Flavors of Canada includes more than 150 recipes. We all recognize the buttertarts, the matrimonial cake and the terrific pickles, but the halibut parcels, the bison carpaccio and the blackberry custard tarts with Alberta Springs rye will open new culinary windows. 
- 2000  Our readers love their date squares. We received many recipes and forwarded all to Julie Kinkaid of Oakville. Date squares are called matrimonial cake in the western provinces. 
- 2012  A down home country meal was prepared, which got us thinking of the role of food in the social and cultural development of this area. One of Blanche's favourite desserts, matrimonial cake, which for decades Blanche took to picnics, pot lucks, church and family celebrations, was enjoyed at the meal. There is some dispute over the origins of the name, but the website The Domestic Goddess (don't we all aspire to those heights), suggests matrimonial cake once had a pastry bottom crust and the name symbolizes the different complexities of marriage - the firm foundation, the sweetness of dates in the centre, and the frequent rough patches in the nubby oatmeal topping. Miss Coultis' date dessert is a western Canadian classic, and we decided the recipe was worthy of a place in the museum archives. 
Images:
Chart 1: Internet Domain Search, 15 Aug. 2012
Chart 2: Regional Domain Search, 5 Jul. 2013